PID tuning and different filament temperatures
PID tuning can be performed multiple times and the results saved for future use, since the question is about &quot;what are the usable ranges for PID tuning&quot;, based on my experience

a slightly suboptimal tuning will not make the temperature oscillate more than 2-3 degrees, which is more than enough for most traditional filaments
if you have a 30-40 °C temperature range you can likely keep a tuning in the middle and be done with it
an accurate tuning is needed if you run the hot end at its maximum rated temperature: mine was rated 250 °C and without a good PID tuning the temperature was overshooting by 2-3 degrees, which was enough to trigger a over-temperature safety shutdown. Using the printer at 245 °C would have resulted in no issues even with sub-optimal PID tuning.

Of course, people with high temperature hot ends (up to 270-300 °C or more) will need a tuning for the usual range (200-240 °C) and one for the higher temperature range to obtain better prints.