All Provoke does is matches your enmity with the person at the top of the list (even yourself), then adds 1 to that total. So if you use it right at the start of a fight, you generate a whole 1 enmity.

If you use it mid fight when you already have established your enmity, it just adds an extra 1 to your enmity, which will be meaningless.

If you are at 0 enmity with an enemy and a healer/dps/tank has 1000 enmity, when you use provoke you match the highest enmity, then add 1, so you would gain 1001 enmity. This is why it's important to follow it up with a shield lob or a comboed savage blade/rage of halone when possible.