What can happen to a pump in a pit without water for many months, then the fall heavy rains start adding water to the pit, will the pump be efficient to do its job? Should water be added to the pit to exercise the pump? If yes, what would be the recommended frequency?
Two issues I would check 1) can the pump prime okay without intervention. An air release valve in the discharge would help.
2) Pumps left idle can suffer from corrosion which causes them to seize when they are operated.Suitable materials and clearances would be required.
A final problem with not using machinery until it is needed is that you don't know if the pump has failed until you need it, at which point it is too late.
Speak with the manufacturer regarding the frequency of exercising the pump. Monthly would seem reasonable
a submersible pump in a sump pit is subject to being fouled by sedimentation i.e., the slow accumulation of sand and silt in the pit during extended periods of inactivity. If that silt gets into the impeller scroll, it will lock the impeller and stall the pump motor; if it fouls the float switch then the pump will not turn on and the sump pit will continue to accumulate more silt and sand. If the float switch is not fouled but the impeller is, then since the pump relies on water flow to cool it while it is running, a silted up pump will overheat and burn out its windings.
The only way to prevent this is by inspection of the pump in its pit and periodic cleanout of the silt and sand.