We talked about letterspacing before, when I said not to letterpsace the lower case. Now we’re going to talk about what it is appropriate—or even encouraged.
Anytime you’re typing in all-caps, it’s good to add some letterspacing. When would you use all-caps? Well, I’m not really a fan of doing it at all, but it’s understandable if you type in all-caps for a header or something like that (not main “body” text).
If you’re using small caps, which I’m a bigger fan of—please letterspace a bit. You’d use small caps for abbreviations more than two characters in length or for titles.
Numbers, too, especially lining figures (numbers that are the height of capital letters) should have some letterspacing.