I was a total disbeliever in defense so much so but explaining should be an other thread now this what I've noticed if you place your defense building near to your money building it harder to attack but for some buildings it dosn't matter example place turrets around a warehouse even if they turrets lvl 10 but if you place just one lvl 10 turret by a flower shop you will notice.
I once went to a hood a collected his brownstone no problem then I robbed a few others then I got to his russian restaurant I lost the fight tried again lost the fight then realised the reason was because next to it was his surveillance center.
This is the one benefit of defense building you won't believe but the defense you have the lest you will appear on the rival list.