MAF sensor replacement=smooth idling?
 

A couple of days ago my SES light came out and the error code of P0172 and P0175 were displayed. My service Advisor in Fairfax BMW immediately got me in the following morning and replaced the MAF sensor.

I noticed after getting it from the dealer that it idles a lot smoother and the engine seem to be quieter. Is this the effect of a new MAF sensor or is it just me?

Yes I think it was likely because of the MAF. that plays a role in the air been drawn into your engine. If that messes up then the air into the engine will not read the same so it throws a CEL (check engine light)