Let's compare the two ailments.
Bind : Halts all movement for the duration of the debuff, Resistance built will reduce the length of the debuff. Actions can still be used while binded. If a player is within range of you you can still attack them/CC them while binded. Tri-bind can be swiftcasted for a 6 second bind.(Originally 12) , GCD

Sleep: Halts all movement and actions for the duration of the debuff, Reistance built will reduce the length of the debuff. Only purify can be used while slept.
Nightwing : Instant cast AoE Sleep , Duration 15 seconds, CD 180 seconds
Sleep : Duration 15 seconds, GCD, swiftcastable.

Sleep is a more powerful version of bind with a longer duration under the same constraints as tri-bind.