Advantage And Disadvantage

In 5th edition D&D, if a roll is made with an advantage (attacking a prone or surprised enemy for example) instead of a big bonus, you get to roll twice and take the better roll. If you are at a disadvantage (attacking from prone position or blinded) you roll twice and take the worse roll.

What I am thinking is that when I give players bonus XP chips for good roleplay, etc, they can give up a chip to take advantage on a roll. I might even let them spend a chip or two to force a NPC to roll with disadvantage.