I've seen this many times, most recently when I was spotting at a small airport in the Lake Region of Finland (Savonlinna, SVL) last summer and the first time a Flying Enterprise (Swedish airline cooperating w/ Finnair) SF340 (ex-Finnair) landed, the taxi way is max 300 meters. As soon as you could see them coming from the end of the runway (turn around at the ends, concrete pads) only the engine opposite the deplaning side was running. This also happened when a Finnair ATR-72 arrived for my flight to Helsinki, again, number 1 engine off. I saw it and wondered "What the heck?" but never thought much about it until now... i would say mostly it's for efficency, turn around times are 5 min. (NOT KIDDING) on these quick flights.
Head in the clouds... yet feet planted firmly on the ground.