I usually just use who I want to anyway, so this was never really an issue for me. On future playthroughs I'll even go out of my way to use the ones I didn't. All apart of the replay value, in my opinion.
For some reason I used to play very first come first serve when it came to units. As in, I would only use the earliest gained units and never any units who came past the usual deploy limit.
One of my favorite games. I was put off by it when I first played it but when I went back and gave it a second chance I was blown away. Also the soundtrack is easily one of the most memorable I've ever heard.
Awakening. Reclassing freedom on Robin. Course I much prefer Fates system of friendship seals, Awakening's style was still fun for being absolutely broken.
I always avoid buying skills because I wind up forgetting about the main story and concentrating on making everyone have a nifty skill set. I figured after I beat each route clean a little new game plus esque style of play wouldn't hurt. Course that just made most of my future runs pretty boring and easy. Gonna agree that experimenting with friendship seals keeps it fun though. Part of the entertainment comes from having units in classes they aren't usually in. At least in my opinion.