Benefits of Premium:
XP lets you research new upgrades for the operator.
Extra XP lets you upgrade any operator you want.
Coins can be used to purchase:
Coins can be exchanged for Credits.
A XP Booster has a capacity of 20,000 XP and gets you +200% XP per battle.
XP Boosters allow earning more XP in battles and accumulating it faster so as to exchange it for Credits.