To reproduce:
1) Make sure you have clean Unity install without Facebook module
2) Open and close attached project a few times
3) Each time, it opens up pretty quickly (<5 seconds)
4) Install Facebook module
5) Repeat step 3

Expected: Load time stays the same as Facebook module isn't used in anyway in this project and no unnecessary process should be called without platform change
Actual: SDKUpdater.exe launches and scripts are recompiled each time, so the project load times are increased due to that (average is either about 15 seconds or 2 minutes, depending on situation)

Reproduced in 5.6.0b3, 5.6.0a6