How should I use Locations?

Solution 1:

Most progamers that use those keys are using them for the bases. Right at the start of the game (after making workers mine of course) they go through main, natural and third and hotkey each of them to the function keys.

For all other locations, unit hotkeys are usually more useful.

You could also hotkey Xel'Naga towers and such but it is imho less useful.

Solution 2:

In addition to what dbemerlin said, you can also hotkey,

• Your ramp. (If your base has one.) This is great for early game micro. It's probably also your first rally points.

• Rally points for your production buildings. Since your units don't come out automatically hotkeyed to control groups, having a location hotkey quickly lets you view them and assign unit hotkeys.

• Future rally points for your production buildings. This might be a Brood War habit. You'll probably want to reassign your rally points as your army moves across the map. You can save a lot of time by planning out locations and hotkeying them. Plus this way you're sure where you set your new rally.

• Opponent's ramp. Great for early game. Can help you micro your scouting worker. Can help you micro your early attack. Quick way to reassign your rally points to the front.

• Opponent's expansions. Helps you keep track of the opponent's expansions. Reminds you to send a scout if you haven't checked it out in a while.

You may notice that progamers cycle through their unit control group hotkeys a lot. You can do the same with your location hotkeys periodically. Since they're all important locations to you, if there's a place that you haven't had vision of for a while, it can remind you to send out a scout.