Every layer saves you time, until it hides the reason something broke. So for your own peace of mind, understand how each layer works.

Should you put in the effort to know a codebase inside out? And if yes, how?

Most people rarely read privacy policies, but that's where most services hide weird behavior in plain sight. So maybe, just maybe, if there was a way you could quickly get the important parts of any policy without having to go through the whole thing, maybe you'd make better, more informed choices, and just maybe, making this knowledge more accessible would help in fighting back against these weird behaviors.