When should I use an Orb of Scouring?

Removes all properties from an item. Right click this item then left click on a magic, rare or unique item to apply it.

What's the idea ? What would be a practical use of that ? I don't really see when such a thing could be useful...

Solution 1:

I've used Orbs of Scouring a couple times so far. The main use of it seems to be if, for example you find a magic item with great sockets, but, still, it's only magic. You can use an Orb of Scouring to remove the magic affixes and return it to normal, then an Orb of Alchemy to turn it into a rare item, making it much more powerful and useful than it originally was.

Whetstones/Scraps are also much more effective on normal items than on magic/rare items, so it is oftentimes worth it to Scour an item back to normal, increase the quality, then use an Orb to return it to its former level. Of course, you won't want to do this if it already has excellent affixes, as the odds of getting them back will be almost nil.

Solution 2:

One of the most common uses of Orb of Scouring is to lower the level of a gem by one level. This can be done by selling both the Orb and the gem to a shop.