Better button consolidation. Linear combo weaponskills don't really have any business being separate buttons, and even branching combos can be reduced. Some jobs see as many as 6 buttons freed up, which, with better slot economy, can see additional weaponskills or abilities added. Using specific examples

Dragoon: Frees up 7 buttons. (Two combo starters, Doomspike)
Monk: Frees up 4 buttons ('Flank' and 'Rear' that change given your current stance)