I use to teach everyone every spell back in the day but I don't anymore. Largely cause I realize I never used magic much for half of them and partly because I felt I always got more "bang for my buck" by specializing certain characters with specific magic builds. It's kind of fun making one character a Time Mage or making Celes into a Paladin, or building Relm into a traditional Red Mage (only low to mid tier magic). It has made the game more fun in more recent years.