When you play a boon that has multiple powers, choose only one of them, even if playing the boon doesn't take it out of your hand. This rule applies even if you are allowed to play the boon freely.
For example, the item Bracers of Protection has the following powers:
When you suffer Combat damage, freely reveal to reduce it by 1.
When you suffer any damage, recharge to reduce it by 1.
So when you suffer Combat damage, you can either reveal or recharge to reduce the damage by 1, but you cannot reveal to reduce the damage by 1 then recharge to reduce it by another 1, even though one of those powers can be used freely.
Some weapons like Daggers break this rule by saying you can use a power freely even if you already revealed the card on the check.