Sap is an effective crowd control technique. Don't forget to tell the party which mob you are sapping, as any damage breaks the effect.
Sap does not cause threat, meaning that if you Sap a mob and then move out of normal aggro range, the mob will not attack you after the Sap effect is broken.
Mobs that are Sapped won't be tagged as your kill until you deal damage to them. Be wary of other players stealing your kill.
Sap can be useful in a PvP environment, to even out a 2-on-1, to take out a Shaman's totems before you fight them, to capture a flag quickly in battlegrounds, or even after a [Vanish]. Remember, like all crowd-control effects, Sap is limited to a reduced duration in PvP.
Sapping a player of the opposite faction will turn on your PvP Flag. Be wary.
Comparison to Paralysis
Upon release, monks were given a crowd control ability called [Paralysis]. Like Sap, this causes an incapacitate effect up to 60 seconds long, but was considered a magical effect that could be reflected, grounded, or dispelled. In patch 5.2.0 it was made physical, increasing the similarity to Sap. This section compares the two.