Not in use? Doesn't mean not important.

Some safety systems like safety interlocks, hotlines, are meant for use only when something goes wrong. 

Some systems like SCBA, we use, with the knowledge of possible hazardous conditions in work areas and as a preventive measure. 

Some like PPE are routinely used as minimum requirement for protection. 

We need to ensure functionality of all, whether we use it or not, by checks, at recommend periods. Else, they will not be available when really required. It is likely that these checks for some are postponed as they are not required immediately or on assumption that it will work as not used means it will be working. 

In another scenario,  if, say, frequently interlocks are in use, implies that something is going wrong and we should analyse the reasons. Jockey pump in fire hydrant system is used to maintain line pressure. If it is auto ON throughout the day implies line leakages or wrong use of fire hydrant.