With mechanical drop sets, instead of dropping down to lighter weights when you reach failure, you keep the same weights but switch to a related exercise where you have a mechanical advantage. This allows you extend the set, triggering metabolic stress and increasing time under tension, both crucial for hypertrophy.
Here's an example for arms:
Start with 8-10 Zottman curls. Curl the weight up normally and then rotate your wrist into a palms-down position to lower the weight.
Now do 8-10 hammer curls without resting.
Finally, rep out with 8-10 alternating dumbbell curls.
The floor press prevents over-stretching at the shoulder joint and eliminates an excessively stretched pec tendon at the transition point from eccentric to concentric, thereby eliminating much of the danger-zone for pec tears.