No we didn't, because on a computer it doesn't require any meaningful extra effort (unless you're a lazy kid -> another age indicator), and pre-smartphones... texting actually used to cost money. You'd probably have a plan of some 1000 free text messages / month, or sth., which isn't that much if you're a teenager, given that a text messages was limited to ~140 characters (yes, that's where Twitter's limit came from - SMS compatibility).

Caps, instead of being waste, let you skip whitespace. Instead of writing "caps are a waste", you'd write "CapsAreAWaste" (and then possibly shorten it to "CapsRAWaste"). We'd cut the message length by some 20-30% this way, which mattered for longer messages - it would turn a 4 SMS long message into a 3 SMS long one. We'd of course optimize harder when we were close to message length boundary.

Being efficient with text messaging was a critical social life skill when I was young.