I use a float switch that screws into the secondary coil drain... IMO to stop the water BEFORE it overflows the coil pan is the first line of defense.
If the unit is anywhere other than on a concrete floor, it gets a pan float switch also.
The condensate pump ALWAYS goes IN the pan, and the switch in the condensate pump is always wired in.
If the install is an 80% furnace (most are in my area), then I break the Y... If it is a condensing furnace, then I break R.
And I always install a T in the coil drain... it gets flushed each spring.
So far, so good... in 10 years NO sheetrock repairs. NEVER have made a claim on my G/Liab policy... lets see if I get to continue this way.