Board Thread:Questions and Answers/@comment-29825745-20160901132252/@comment-26871105-20160902022828

Enhancement is about enhancing the quality of something that belongs to the user, be it their trait or their immediate possession.

It can be applied offensively and defensively, depending on the user's desire and need. The only thing that might give it a bias is dependant on the user themselves, whether or not they have an unconscious bias towards either of them; even Netero who had perfected a balance between both offense and defence showed a very slight bias towards one of them, which led to his defeat against Meruem. But that's not because of the Nen type itself has some pre-determined bias.