Cloud? Airspace? Only just left airfield of departure and not had time to climb yet? Shortly to arrive at destination, so descended to overhead join altitude? Makes the plog easier, since there's no need to take into account the different speed in climb/descent if not much time is spent climbing/descending? Only a short flight, better to cruise at low level at 100kt than climb at 75kt? Training flight, instructor doesn't want to waste student's money climbing to 5000' when the exercise can be carried out safely at 2500'?
And, following on from the last one, possibly: all my training was done at 2500', so I find it much easier to recognise features on the ground at this altutide - when I climb higher, things look different to what I'm used to?
I'm not claiming that all of these are necessarily good reasons - just that they're possible reasons. And I'm sure I've missed a few off, too!
FFF
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