In the Southwest virtually all 120 volt air handlers are plug and cord connected. For years we installed one of these:

With all the newer units having built in motor overload protection it is my understanding that the fused receptacles are no longer needed/required. I believe this is also true of evaporative coolers.

Anyone have any input on this?

Here furnaces and air handlers are hard wired; OCP is the branch circuit breaker and/or internal from the mfg.

A lot of the furnaces in the Midwest have a similar device to the picture, but with a switch instead of a receptacle and the furnace itself is hardwired. A service tech told me that's so he can unscrew the fuse for LOTO instead of just hoping that the homeowner doesn't turn the c/b back on.

In a lot of the older homes around here, they used to use them for furnaces and boilers as well. Usually the service was 100 amp and fuses.

I've installed a few of those, as a way to give the equipment more appropriately sized over-current protection. I'd use an Edison-base breaker, rather than a fuse. Only problem is ... they didn't work out.

They didn't work out, as the first thing the HVAC guy did on his next visit was remove them, leaving an open box in place.