Does System Integrity Protection have any effects on OS's besides Mac OS? If I understand correctly, SIP is a security feature that protects certain folders on Mac OS from modification, even by root users. 

I don't know how it works on a low level though, and I was wondering if enabling/disabling it has any positive/negative effects on other OS's installed on a Macbook, such as Windows or Linux distros. So, does it?
No, SIP is only applied within a macOS partition. You can have a look at /System/Library/Sandbox/rootless.conf to see which folders and files get protected by default.