Keeping an organized buddy list will help you find buddies when you want to IM them or see if they are signed on.  As your buddy list grows, this will become more important, especially when you have to scroll down to see all the buddies on your list.  You can organize your buddy list manually, by dragging your buddies up or down, into the order you want them displayed.  You can also automatically organize your buddies alphabetically by clicking on the "List Setup" tab, right clicking on the group of buddies you want to alphabetize, and then clicking "Sort Group"