Run REW prior to treating room

I to am to use REW with little experience of it as a software. 

Any guidance on its use will be appreciated. 

I will be programming Hypex Amp's to work with Bass Units. 

Yes you need before and then after data to know which treatment is working ideally.

This video series is awesome for that even if the primary focus is studio spaces. The general understanding cuts across to home spaces too

Here - https://youtube.com/playlist?list=PLsyXZjufQdPzWqlRg2TtGWQ529z5noERs&si=6aWkhtCnpM54c--X @grunge1000 @pindac 

Thanks @kofibaffour 

Yes, before and after every change you make.

Just remembered that GIK will take your REW measurements from your untreated room and make recommendations for you.  It’s a free service and no required purchases.  At least it was when they did it for me.