You will know when it’s time to set the saw when it binds in the cut while sawing.
The teeth are bent outward to provide that clearance.

A saw set is nice, but not absolutely necessary. You can set the teeth with a nail set or punch on a scrap of softwood. Paul has a couple videos on doing that. Here is one:

The trade off is you need a little skill to set the teeth evenly, but it’s not rocket surgery.