Why not leave an electric fuel pump on all the time? This question is related to single-engined piston airplanes equipped with an electric fuel pump like the Piper Dakota/Arrow etc. The POH states that the fuel pump should be switched on for takeoffs/landing/approach and maneuvers. 

I understand that the fuel pump is a backup system and switching it on provides an extra margin of safety in such situations. My question is, why does the POH recommend that we switch off the fuel pump after reaching a safe altitude (say 1000 ft). Wouldn't it be safer to just leave it on? Is there potential for harm in leaving the electric fuel pump on? Or this is done on common sense grounds: just to save maintenance and prolong the life of the backup system so that it is there when you really need it?
The electric fuel pump is used to provide an extra safeguard against fuel starvation during critical operations in siphon fed fuel systems where either there is an increased risk of this happening or where sufficient altitude does not exist to resolve a problem such has switching fuel tanks or during takeoff and landing operations.  While one could in theory continue to operate the electric fuel pump continuously throughout flight operations, it it not necessary and just adds additional wear and tear on the unit.