Hmm I think I got it. It's wise to promote your characters about level 25. Because when you're 20, you gain lots of xp from powerful monsters (such as catapult etc) when you're promoted you gain half xp. But after level 25 your xp gets lesser than promoted battle victory xp amount. And for many characters promoted level ups are much better. I'm not a guy who will cast egress 100 times and level up all my party to level 99 I like to egress only few times just for fun

Any other suggestions about SF2?