On 737 these lights are also emergency lights,being on the baterry bus.You'll be amased how many pilots,keeping them off,forget about them in simulators in case of total electrical failure,and try to use torches to see the things around them in the cockpit.
The sop states to keep this lights on,eventual on dim position.
Also,at night,it's better to keep the lights on,regarding eye fatigue.These nice new displays are ok,except they tend to affect your sight,little by little,especially at night,in a dark cockpit.
During daylight,it is discussible,indeed.Why keep them off? Save bulbs,eventually.I can't see another reason. (save electricity
?)
Brgds Alex