I use to stop two engines when taxi in if I have to wait for the parking or long taxiing
(A343). The only consideration is the hyd for the brakes (Y elec pump on the A320) and very important to wait at least 3 minutes to shutdown the engines. The same aplies when taxi out. The more important cuestion is to warm up 3 minutes before aplying TO PWR. On the Bombardier CRJ it is very usual to taxi on one engine because you have to be braking all the way up, or using the reversers, with two engines at idle. There has been a Bombardier circular about a company that broke one engine two times during the TO. The circular explained that it is important to warmup for the rings of the turbine axis to get its work temperature and seal correctly. Otherwise you can damage the engine and loose it during the TO
