One place you clearly don't want the mag disconnect is in competition, but only because of the awkward process of clearing the gun and then having to insert an empty mag to do the required hammer drop.
I got literally tackled by an RO in USPSA who obviously thought everybody should shoot 1911s and never heard of a mag disconnect on a Browning High Power.
When clearing a gun with a mag disconnect, be sure to drop the mag, then clear the chamber, then use an empty mag to drop the hammer.
A friend put an empty mag into his gun and killed his washer with the cartridge that had been left in the chamber.