For my usecase, it’s mostly been checking that Voltages and Currents align with what I expect them to be, checking components to see if they are what I think they are (e.g., Resistance of resistors, whether Diodes are faulty or not), checking whether two points are connected, checking whether signals into and out of microcontrollers are as expected etc,. Things like that off the top of my head. Though I’m probably only scratching at the surface of what they can be used for.
Doing a bit of a deep dive into some forums, it seems that paying more will get you better accuracy, but the more important thing is that the real cheap ones most likely don’t come with a lot of protection, which is okay for when your looking at 5v type stuff, but if you want to look at anything to do with Mains voltage etc, comes into play.