I don't think I could bounce the bar off my chest if I wanted to. I've spent so long learning to wind up the tension as I control it down that I'd do myself an injury if I tried to bounce it.
The spotter's job is to save your life not do the lift for you. If he touches the bar at all then it's a failed lift, no matter how much you curse him afterwards for stepping in too soon.
Here's an interesting study done on the partner-assisted benchpress:
Partner Assisted Bench Press
Contrary to popular belief, the Partner Assisted Bench Press PABP actually originated in Berlin Germany in the year 1935 by accident. (1) A monogamous couple, Anita Spaht and Ken I. Spaht, were training for the Olympics in their hometown the prior year. Anita was attempting to perform multiple repetitions on the flat bench with a weight too aggressive for her ectomorphic frame to accommodate. Out of necessity, she reluctantly requested Ken's assistance as she completed partial, multiple sets and repetitions. (1) It was the following 2 days after that workout when Ken noticed delayed onset muscle soreness in his, traps, biceps, and lower back. (2) He then began to incorporate PABP's into his routine to assist in maximizing hypertrophic changes and strength gains in both his squat and his deadlift. He later decided to decline his qualification number in the 1936 Olympics and take up bodybuilding.
It wasn't until the year 1975 when the PABP became recognized in the United Sates. Individuals became bigger, stronger then ever, especially with anabolic enhancement. In the late 1990's until present time, popularity increased exponentially. This was largely due to the opening of numerous fitness facilities across the country. Electromylogram studies illustrated the majority of the muscles used are the paraspinals, biceps brachii, upper portion of the trapezius, gluteus maximus, and the rhomboid major. (3) Biopsy studies showed an increase in the cross sectional diameters of type 1 as well as type 2 twitch fibers. (3) What is advantageous is that it requires minimal effort on the athlete that is receiving the spot so he or she does not spend the energy requirements of the rest of their strenuous workout. (3)
1. Spaht I. Kenneth, Coyle EF, Fink WF, et al: Adaptations in Skeletal muscle following strength training. J Appl Physiol
1979:46, 96-99.
2. American College of Sports Medicine: Guidelines for Exercise Testing and Prescription, ed 5. Baltimore, Williams & Willkins, 1995.
3. American College of Sports Medicine: The recommended quality and quality of exercise for The Assisted Bench Press Med Science Sports Exerc 1990;22(2):265-274.