A few times i have been on a 733 or other A/C for that matter with U/S APU's.
As been said its good to have the GPU connected and started on arrival before the engines are shut down, so it doesn't plunge into total shutdown especially at night
. It happened to me before in PMI where the engines were shut down and all the electrics went off as the GPU decided it wanted to play up for a for a few minutes
.