Hi, there! :)
Hi 5546_student,
"Is it okay to have bad topology and overlapping polygons if the results look good?"
Yes, absolutely!
(I wouldn't even call it bad Topology, but that might be because of my math background...)
I'd say it all depends on what you end up using the model for. If you are just doing it for yourself, so personal use, you can work as dirty as you want. But when you're on a team and on a pipeline and the company has rules, then you want clean models. Good topology offers flexibility, so when it times to make changes, you want a good model that is not going to be a hassle.
So you can have "bad topology" if it works it works if the end result is a great render and no one is going to go into your files but you. Also sometimes you have to work fast, because there's tight deadline, and there's no time for prettiness and you have to slash and hack.
It's always good to strive for clean topology, everything is named correctly, clean UV's etc. When you're able to then for sure it's a rule of thumb, but it's not an absolute necessity.
As you model more and more you'll start to see the pitfalls, you'll see what to avoid, what to be permissive with, what you should and should not do because you know is going to bring you trouble down the line. Go it time, experiment, make mistakes, develop a sense for it all, be patience and have grit, 3D is super fun.