Having been raised with non-regulated irons, know it can be done. You just have to get the touch, and use far less contact time than an iron that is cooler.
However, setting temp limits came out of studying failures that gave us the MILSPEC and aerospace standards that became the civilian IPC standard.
Overall, the bottom line is simply:
Keeping your temps under 350C prolongs tip and heater life
Reduces risk of failures on soldered components
As modern components are smaller and fragile, excessive heat can easily be applied by irons that are kept hotter than ~350C. Many data sheets tend to specify the soldering limits, for example ~300C for 10 seconds or less; this isn't linear and it doesn't mean it can take 400C for 7 seconds.
The manual adjust ability on irons basically compensates for tip wear and bring it back into spec; its not really meant to pump up the heat for large ground planes but you could do that. Its better to use a tool or tip better suited to that that wear out a tool designed for fine work.
Analog adjustable irons use a sensor far from the true tip, its usually near the base, so the reported temp is not the tip temp, so calibration compensated for this error; tip wear can cause less conducted heat, the heating element weaken etc., all require readjustment. A need to 'recal' with each tip replacement is to compensate for different tip geometries: larger tips can report lower tip temps if the station was calibrated against a smaller tip.
You only need to recal if you must know the temp for certain, and if you have a machine that makes it convenient to make such tests easy.
In practice, as the station ages and gets off-cal the practical result is that the soldering becomes difficult, so you bump up the adjustment without cal. I suspect that its highly probable that the measured tip temp is closer to a calibrated value if it were formally calibrated, if adjusted by an experienced user.
For non-production labs, one can easily check if the tip melts eutectic solder, since it goes to liquidus within 1C, to field calibrate a tip without resorting to a tip thermometer.
There are self calibrating stations which have sensors essentially at the tip, such as with Metcal, and there is no adjustment. The station will generate up to its rated power to maintain the standardized tip temp, even if touching a large heat sink such as a ground plane.