There have been a couple of playthroughs where I balanced my team, but I'm normally terrible about it.
I overlap a lot, because I love fire types, and so I tend to use two or three fire Pok?mon a lot of the time.
Or two electrics, or two flying.
By the end of the game, my team is a mix between Fire, Electric, and Flying, mostly. Maybe a Psychic type in there somewhere. I pay attention to secondary types, though, and I give them certain moves that are handy against their weaknesses. They're uneven but I always manage. It's a little weird, but I've never used many Normal or Ground, or Rock mons. They generally don't appeal to me much, and unless I come across one I really like (Aggron, Rockruff, Tyranitar) I don't usually raise them.