Just wondering because I see a lot of guides using it at various points....but I dont understand why.

To me it seemed like its only use would be to reset Iai so you could reapply your dot, or during a boss transition where you wanted to rest your rotation with some extra kenki.

The I see it is:

Kaiten + Midare = 720 + 360 = 1080 potency

Hagakure + lets say 3 Shiten = 300 x 3 = 900 potency

Or

Haga + Guren = 800 potency

So why would I ditch 3 sen and turn it into 900 potency when I could use 3 sen and turn them into 1080 potency?