Most of the heat in a transmission is from the converter. Converter design, stall speed and slippage, sprag or not, etc. effects it. How you run the car, foot or transbrake, 2-step or not, etc.,is the biggest influence.

Why monitor trans temp? Just to try to avoid or detect damage? Change the dial according to how hot the oil is? Or to try to maintain a specific temperature for consistency?

The oil coming from the converter is what it is and usually spikes on the starting line when it's slipping the most. I don't know anyone who monitors just that. Bracket racers may monitor the trans temps with a sensor in the pan and adjust the dial or throttle stop accordingly. But some of the guys who bracket and .90 race seriously, monitor oil temps in the engine and the trans, and have heaters and coolers for both so they go into the water at the same temp - or as close as possible - from the first run of the day to the last.