Does my furnace and water heater need a shut off switch
NEC Articles 110.25, 422.31, 422.33, 422.34 and 430.102(A) provide requirements for disconnects used to protect those who might need to service equipment. Basically it requires the following.


It must be with in line of site and less than 50' from the equipment.
The disconnect means must be able to be lockable for hardwired or plug and cord.
Many AHJ have also require the access to the disconnect to be in an unencumbered path from the equipment.


Also as mentioned by Jim Stewart, it is there for safety's sake and it is rare these devices go bad.

Hope this helps.