The theory about using protected cells is absolutely right but you must also remember that there's sizes for which protected cells are simply not available (e.g. 10440, RCR2, 10180). If you take a Lummi light for instance the only available alternative is a non protected li-ion cell, there are no primaries of that size.
In this case the best solution IMO is to always keep the cell well charged. In my wife's Lummi Wee I put a freshly charged 10180 every Sunday morning regardless of how much she has used the light. Some weeks she uses another light but I still change the cell in the Wee.