When should I be taking the time to identify items, and which items should I not bother with?

There are plenty of guides on how to identify items, but I can't find any on when to bother with it. Certain levels may have many of the same type of monster which will drop much of the same types of items (ex, mines). Turn management can be critical in many places, say, bad circumstances, early game, little food, low-apport pets, weight considerations, etc.

Obviously, this can be highly circumstantial - say needing a particular drop - but I'm more interested in the best general approach to the best general bell-curve of turns/circumstances vs items. I'm also interested in addressing the item hoarder's fear: "I didn't try on every [common monster]'s drops - what if I missed something good?"

When should I be taking the time to identify items, and which items should I not bother with? What about cursed items? What about shops, which can have a wide variety of items? What about when there are hordes of the same monster?

Turn Management

Monsters never stop spawning and your stomach never stops churning. Identifying absolutely everything is not a good strategy, especially when resources are lacking.

"What if I missed something good?"

There is always the fear that you might have missed an item. But this game is not designed to obsess over an equipment that might or might not be more useful than your current gear. Read up on speed-runs to think about how little other players have ascended with.

Even with Bags of Holding, weight is a serious issue. It isn't worth lugging everything around the dungeon to identify it. If you cannot identify it conveniently, leave it as is or stash it away and come back to it later if you still need a better gear later. After all, you may find something very nice in the future. Remember, stash, stash, stash. Don't lug everything with you.

Item Rewards : Always

Certain areas, monsters, and events come with particular loot that is always worth identifying. Consult the wikis for more info.

Cursed Items : Sometimes

It is only worth the time to carry around and identify a cursed item if you know what it is already and still want it. Which means uncursing it first.

Amulets : Always

Amulets are rare and can be quite valuable.

Unusual Items : Always

Some item types don't show up very often, so when they do, it's worth investigating. For example, snow boots, gloves, capes, tools, etc.

Weapons : Rarely

You don't want to spread your #enhance points thinly, so you generally only want to take the time to identify items of the class you wish to major in.

Armor: Sometimes

Nethack randomly generates loot, so even though you just killed 25 Uruk-Hai and they all appear to have dropped the same cloaks, short swords, iron shows, orcish bows, and shields, they are not the same at all. There may very well be an enchanted item in there.

You should check it if:

• it wasn't typical monster loot
• it's reasonable that this armor might have a higher enchantment, or provide better AC
• the item might have an extrinsic attribute

Potions : Beginning-game: Rarely Mid-game: Always

If you have many of a same type of potion, its likely to be a healing potion, but other than that, it's just too risky. Smoky and milky potions could contain a djinn, so it may be better to save them until you can bless them for better chances of a wish. Other potions will be identified gradually as they're thrown at you. Generally serious potion'ing begins once you've obtained a unicorn horn mid-game.

Scrolls : Beginning-game: Never Mid-game: Always

Any desirable permanent effects from scrolls are generally better used mid-game when your inventory becomes more stable and less fluctuating. Except for scrolls of identification, which will generally be the most plentiful.

Wands: Always

If you know a wand is uncursed, it is always worth the time to identify it

with an Elbereth engraving.

Wands can very well be a "Wand of Nothing", so wands that cannot be identified as above are usually more situational and less useful to be carrying around - stash those. Remember that there are some wands you do not want to put in containers.

Rings: Always

If you can BUC test a ring, and know it is uncursed, always try it on. Beginning-game, if it doesn't immediately identify it's likely situational and not worth wearing due to the hunger penalty.

Spellbooks: Beginning-game: Sometimes Mid-game: Always

Beginning-game, there's little room for vast stat improvement. If you're a class with low intelligence, its more likely you'll cause the spellbook to crumble upon reading attempts, netting nothing but wasted turns. If you have an unsuccessful read, it's very likely the next attempt will also be unsuccessful, so stash for later.

Gems: Rarely

Most gems you pick up will be garbage. They take up weight and inventory slots and don't sell for much. Generally they're only worth hauling around for unicorns or shop-keepers.

Tools: Always

Tools auto-identify. If you know it's not cursed, try it out to find out which version of the tool it is.

All wands (even cursed ones) can be Engrave tested fairly quickly and reliably (the wiki explains the details), jewels can be tested by engraving (if asked "what do you want to ENGRAVE?" it's a hard/valuable gem (and thus can be Called), otherwise it's soft and may/may not be valuable (name it SOFT, and it will help sort colors by type --again Wiki). Both tests take little to no time if you do not actually write anything (gems never take time in game) Rings and amulets are worth trying on if uncursed, although most don't auto-identify and may take some time to discern. It's never a good idea to try on cursed (or BUC unknown) jewelry,armor, weapons, or weapon-like tools without some means of uncursing. Many tools carry a risk to testing (particularly in stores and tight spaces) Horns of fire and cold can bounce, other instruments have less danger. Quaffing unidentified potions and reading unidentified scrolls and spellbooks can be wasteful or dangerous. Find a store and price check these items (remember to account for charisma, uncovered shirts, and Tourist status if necessary). This leaves armor and weapons. If BUC is known to be uncursed, it may be worth your while to test armor, especially after clearing a barracks, or other special room for an upgrade (I've found armor up to +4, even some magic armor). Named monsters can be wikied for an idea of what they usually possess. The toughest call is weapons. As a general rule, stackable weapons will generate +0 in abundance, so it's the uncursed oddballs that don't stack that are worth trying. If you have a stethoscope and some patience, you can hit/test/switch/hit/test for average damage (get an average of at least 3 hits per weapon).
Otherwise, unless you absolutely need it now, put it in your knapsack or stash for later (it'll keep).