Soldering

Nah, mostly a thing just for the stubborn points, but a lot of parts unfortunately have to connect one way or another to said stubborn areas, as that's where they get power.

And those traces are typically way larger, even if you don't immediately see those traces, they can be buried in one of the middle layers of the board.

Different materials have a different thermal expansion/contraction rate, so it always helps to try to even out the heat level on the board, hence the reason to preheat it.

It's never good to try to suddenly put 430⁰ Celsius on one spot of a board when your room temperature might be about 30⁰ Celsius, that's a huge temperature change for any one focused spot.

You want the board overall to be pretty warm (and dehumidified if you're really getting serious like reballing a chipset or something), but yeah, stubborn spots like to be preheated.

It also partly depends on the type of solder being used, older lead based solder melts at lower temperature, but lead based solder is practically obsolete these days. Most solder these days is tin based, which has a higher melting point.

In my experience with soldering, I've found the temperature range between 370⁰ to 420⁰ Celsius to be sufficient, but when I have to crank it up to 420⁰ I'm already worried.