Ever notice that the forends for the police 870 are shorter than for the field guns? My arms are toward the short side (32" sleeve) and I tend to grip the forend toward the back. So I prefer the added length of the field forend -- to avoid getting bit on the heel of my hand when cycling the action.
Sure, I could reduce the stock length, but the field forend takes care of the problem and I've shot this length of pull on Remington's for 40+ years.