I notice my furnace and electric water heater have switches. Why do they have a switch, is it for convenience or are they required by code. Each of these are on a dedicated breaker and the breaker panel is only 15 feet away. The switch just seems like another thing that can fail.
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.