[AFMUG] does SM ext gain setting matter in 5.7 GHz?

[Ken Hohhof via Af]

At the AP it matters because of regulatory limits on EIRP.  In DFS 
frequencies it matters for the DFS algorithm.

But if you forget to set the external gain on a 5.7 GHz SM when you add an 
external antenna or reflector dish, does it matter?  Is there something in 
the performance that is affected?