Local 101: Newbie Learning Questions

I’m pretty new to Wordpress and web development in general, so my lack of understanding may just be because I’m a newbie. However, I’m frustrated by the lack of documentation on how to use Local. I’ve been learning how to use it in a trial by fire way. What I’m wondering about now is regarding the Dev mode; when am I supposed to be using it? Why does it matter? What does “disables the Varnish caching layer” mean?

Any other tips for properly using Local would be great, as I clearly have no idea what I’m doing. P.S. Flywheel, I would love it if you could put together some documentation!