Thief FAQ
What can Fast Hands do in the 2014 rules?
Fast Hands expands Cunning Action so the Thief can use a bonus action for a Dexterity (Sleight of Hand) check, thieves' tools to disarm a trap or open a lock, or the 2014 Use an Object action. It does not automatically allow every action involving an object or magic item as a bonus action.
Sleight of Hand
The bonus action can perform a Sleight of Hand check, making pickpocketing or similar manual tricks much easier to combine with the Rogue's normal action.
Thieves' tools
Opening a lock or disarming a trap with thieves' tools can be attempted through the bonus action when the normal conditions allow the attempt.
Use an Object
The 2014 Use an Object action can be moved into the bonus action. This can make mundane adventuring gear much more tactically useful.
Magic items are different
An item that specifies its own activation action is not automatically converted into Fast Hands merely because it is an object. Use Magic Device at 13th level changes requirements for using items, not the activation-time wording of every item.
Action economy is the real power
The Thief can often interact with the environment and still use the action for a Sneak Attack weapon attack. The value therefore depends heavily on whether the player looks for useful objects, traps, locks and terrain.