Regen (AKA regenerative braking) converts the kinetic energy (Energy from the mass of the user moving) into electrical energy. Mechanical brake system (Friction brakes) converts the kinetic energy into heat; this is a very inefficient way of stopping a vehicle energy wise. In simple terms, the motor is converted to an electrical generator when the user applies the brakes. Part of this generated energy is pushed into the battery recharging it and part of it is dissipated into heat.
TLDR Regen Braking:
Extends the range of the scooter
Make the mechanical braking system last longer
Have typically much smoother feel than mechanical brakes
Does not negatively affect the motor
Can increase the heat of the controller but does not negatively affect the controller
We have electrical systems in place to stop it from overheating above our set threshold