Boeing do not recommend taxy out on one engine but have no problem taxiing in provided all factors have been considered. Then again in JFK with upto 3 hours at the holding point and a lot of creeping it would make sense to taxyout on one.
My airline (LCC), wants us to start APU taxiing in, only if the delay on stand will be more than a couple of minutes. We use about 6kgs/min/eng 737. The APU uses 2kgs/min 737. Also we do not care about the stop/start cycle of our APUs because the maint price is fixed with a third party. Fuel is most airlines single biggest cost, so saving it is paramount.
On a side note, the rush mentality around LCC turnarounds is ludicrous. Everyone is on a bonus to be speedy. Occasionally this turns into haste and cargo doors etc are opened whilst engines are still running. The best reason to single engine taxy in is to reduce the odds by 50% of sucking in one of those poorly trained baggage handlers! Trust me, just like the Helios accident was entirley predictable, the next accident will be a suck in on a LCC turnaround!!