Edge is the total fifth wheel in the final party of ff4. Cecil and Kain deal big physical damage. Rosa and Rydia kick butt with magic. Edge does moderate physical damage and can throw stuff, and use mediocre magic. He is useful as a damage tank and the extra physical attacks are nice, and a well timed throw can salvage a lost cause of a battle. But really, Edge is the least important character in that party. Yang, by contrast, is hugely important during the time he is in your party, and he sacrifices himself to save the party, and his wife is a bad ass too.