Gate resistance in mosfet and base resistance in bjt

[Rajnaveen]

Why we place a resistance between gate to source and how to calculate it?
Why we use base emitter resistance in bjt and how to calculate it?

 

[Audioguru]

A gate to source resistor for a Mosfet turns it off when the power is turned off and prevents the buildup of static electricity. It can have a high value depending on how long it takes for it top discharge the capacitance.

A base-emitter resistor for a transistor usually has 10 times the transistor's typical base current so that the circuit will work fine if the transistor has an hFE from minimum to maximum.