User blog comment:Fliu/My Thoughts on the Dressrosa Arc part 2/@comment-10543621-20150605000443

Doffy not using parasite more often has always been an issue to me. The argument I've used to convince myself is that attaching parasite strings is considerably more complext than say piercing a hole in them or slashing them. So that limits the times he can use parasite. Opponents that are fast enough and are guarded are most likely able to deflect/avoid the parasite strings.

So far, Doffy has used parasite on people that are either significantly weaker than him, or were caught off guard. Bec was kinda both.