When it's hot during the day and cold at night, I sometimes find myself under-dressed for late evening riding. I can pedal harder to generate body heat, but on flat ground that creates wind chill & doesn't help. Pedaling hard while lightly holding the brakes works really well to warm up!
But the downhill-biking folks warn about the hazards of overheating brakes (mostly disc brakes but also rim brakes / V-brakes). I have V-brakes.
I imagine just pedaling into brakes transfers heat into them much slowly than controlling downhill descents, since I can go down hills much faster than I can go up hills (it takes much longer to transfer one hill's worth of energy from my muscles into having climbed the hill than to transfer the same one hill's worth of energy into the brakes/rims while descending it).
Do I need to worry about this at all?
It's functionally impossible to overheat bicycle breaks. It's been tested, and the energies involved just don't get to temperatures that high.