Some are used all the time; some are used only when the motor fails; and some are not necessary. It all depends on the slide manufacturer and the system used to open and close the slide.
I have found:
Lippert electric motor drive with gearbox and internal clutch - required all the time as the clutch can slip under side/centrifugal load and release the slide.
NORCO motor driven gear gearbox and steel cables - needed only when gearbox fails and needs to be removed to close the slide for transport
Schwintek slideouts - required only when gearbox or motor is removed.
Hydraulic slideouts - recommended as cylinders can leak internally and release the slideout.
Mine in use; you of course, can do anything your heart desires.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW