I don't agree with reserves, cause what if you're in a predicament when your first party gets all KO'd, you can't really rely on guys who are 30 levels below to kill off the enemy, unless you're thinking to put two of the KO'd members in the team, revive them with the reserve and that's it.
So really their supporting characters? I respect that...but I also prefer having all my characters equally at level 99...looks and feels better, and completed.