Fox12 said:
My question is about the the defenses. Does anyone ever raid your settlements?
Yes, your settlements can come under attack off-screen. You'll be notified of it via an objective in the Misc section of your quest journal.
However, settlements with no people in them don't appear to ever come under attack (this could be wrong though; more testing is needed here). And also, settlements with a high 'defense' stat don't get attacked either.
So yeah, setting up turrets everywhere
does help, insofar as it prevents the settlement from being attacked (or vastly lowers the likelihood of an attack happening, rather).