Mechanical drop sets (unlike regular ones where you just reduce the weight as you fatigue) allow you to switch to an easier modification of the movement, usually with the same weight. This helps you to increase metabolic stress and time under tension; both of which will stimulate hypertrophy.
Shoot for 3-4 mechanical drop sets for each muscle group. Then call it a day.
Biceps
Set up at a preacher curl station with an EZ-curl bar. Load it up with a weight that you could curl 12-15 times.
Knock off 8-10 reps on the steep, vertical side of the bench. Hold each rep for a 1-second peak contraction.
Swing around to the angled side of the bench and try to match the rep count from the first part of the set, with a slight pause in the stretched position on each rep.
Last, rep out for as many standing curls as you can with the same bar.
Triceps
At a high pulley cable station, complete 10-12 reverse grip triceps extensions.
Next, flip around and match that rep count with overhead triceps extensions.
Hold for a 2-second pause in the stretched position on each rep.
Finally, face the stack one more time and hit as many regular triceps pressdowns as you can.
Forearms
Start with 8-10 Zottman curls. Curl the weight up normally and then rotate your wrist into a palms-down position and lower the weight.
Follow that with another 8-10 hammer curls.
Rep out with a final 8-10 regular alternating dumbbell curls.