Provided you have good eyesight and steady hands, I've mostly found what happens as you get smaller is:

- Heating becomes easier. There's no large sinks to take the heat away.

- The solder's surface tension does more of the work. It feels a lot more like sticking together things with tiny droplets of glue. Having the correct amount of solder in the right place is critical.

- learning how to brace your hand against something in a way that gives you very fine control. One reason soldering with an iron can be difficult is because your hand is so far away from the tip, like trying to write with a pen held by the end.

I don't think that modern boards are really repairable at all beyond component replacement- 4+ layer stackups being the big reason. If there's a way to do anything to those boards besides total replacement I'd be super interested to know.

The techniques here are also way beyond basics I think- like, you look at most guides for repair and it's "idk just solder some bodge wires on there, here's what a good joint should look like"

It's great for working on vintage equipment, stuff that might need (and warrant) that kind of repair. Less so if you run a cell phone repair shop.