Under dash twin speakers

Just out of curiosity, any reason people are running the twin speakers as opposed to a single? Years ago my brother had a 69 Charger with the center front speaker and we found a new one that fit, I think it was a Pioneer. It's a weird size, but I think they may still make them. I imagine the twin setup gives you more options though. We ended up hanging on to the speaker and I put it in my Dart without any trouble.