Theres no such thing as no drops 
but the caps help to sustain big current draws from the load, absorbing fluctuations in voltage both up and down. (Yes, when the mosfets turn off or you apply break, transients up is present, the motor is essensially a big inductive coil that is very volatile when exposed to switching)
Generally more cap is better but theres alot of factors in play. If you draw current long enough the energy in the caps will disipate very quick. But the transition from drawing current in caps → battery becomes alot smoother.
I remember calculating an semi ideal number for amounts of Farad on the caps and the trade off reaches its peak around 1200-2000uF or so for the Vesc6(on the electrolytes). Meaning above wont yield alot more benefit.
Drawing more current quickly => more energy => more cap needed.
Theres also alot of math surrounding ESR of the caps. Which is why a mix of lytes and ceramic is very common and often beneficial.