Most characters, once the reach a high enough level, or receive enough gold, or find heavy armor, begin to wear it. Plate mail is a classic example of heavy armor. Though it comes with a high AC bonus, it comes with a severe armor check penalty, as well as a very low dexterity modifer (+1 or +0 :( ) Based on this information, if your character has a high dexterity modifer, you probably don't want to give him/her plate mail due to the dexterity modifer restriction. As I always say, consult the Player Manual to see specifics.
Growth and Drowth are one