In my opinion, for taxi out it's a bad idea. An engine fire (uncontained) during start-up and you'll be a long way from the fire extinguisher and possibly on a congested taxiway with other aircraft either in the way, or blocking the way for the fire trucks.
Shut down an engine or two during the taxi in still has risk, but that risk is mostly confined to the probability of a tailpipe fire which can be handled by dry cranking.
Just my two pennies worth.