What's the point of having /usr/local on it's own partition?
 

This is one of the partitions I see in almost every partitioning guide and I don't get it. Why would you have than any any partition other than the one /usr is on? The only thought I've had is that since it's using binaries compiled on your computer, it might be more tuned to your computer than your OS so when you switch distros it would still work (provided nessisary libraries.) Other than that, I'm lost.

Usually /usr/local contains self compiled binaries, as you say. If you forever reason have to re-install the OS (not a different OS) it may be convenient to not have to recompile your programs. Of course, if you make proper packages of the software you want to install and backup those packages this is not needed, also not if you have backups of the /usr/local directory or just don't compile software.

A separate /usr/local makes more sense on the traditional commercial UNIX OSes where one may have good reason to isolate additional 3rd party software from the Vendor supplied stuff. On your average linux distro, most software is packaged to go directly into /usr and /usr/local doesn't serve quite the same purpose.

Personally, I just use /usr/local for my own locally written scripts/programs and anything from 3rd parties either goes in /usr (under control of the package management) or into /opt.

I guess the reason it gets suggested so often is pretty much the same as the reason people tell you to have swap of 2x RAM: they heard it somewhere and are just parroting what they've heard.