Sometimes too much power available for cruise.
Some aircraft which operate at lower altitudes have their engines operating inefficiently at low power.
In these circumstances it is a technique to close 1 of 4, or maybe even 2 of 4, down so that the operating engines will be at much higher power up near their best efficiency.
The P3 maritime patrol aircraft is one where this is done often to extend patrol time.
Probably done too with turbojet powered maritime aircraft.
Any others do this routinely?