next time your in the gym do an experiment,, if you bench 315 for 8 reps- then you need a spot to get 2 extra reps.. instead of the forced reps, do a drop set and see how much weight you would need to take off to get 2 extra reps with no help... for me i would need about 40 pounds off the bar.. so that means the spotter would be taking off 40 pounds