Mike Walker
Contributor
some say not turn your light off, it may not turn back on....simply hold it against your chest or cover it with your hand..
This was probably a lot more relevant in the days of replaceable lamps (lamps die most frequently at turn on).
LEDs can fail but the odds of it happening are much lower and many lights have multiple arrays and such making a single catastrophic failure very hard to achieve (without something happening that would kill it anyways whether it was on or off).
With modern LED based lights I wouldn't worry about the on/off cycle. Having a full backup is a good plan, however.
(That being said - there are still old lights out there so actually check before assuming a borrowed light will have the reliability of LED. My thoughts are based on what I carry.)