Are there any risks or disadvantages to building software from source, compared to installing a package? Can it mess with my system in any way?
I usually avoid it because I’ve found it to be a faff and often doesn’t work anyway but in a couple of cases it has been necessary.
Think about it this way: you’re downloading someone else’s code and running it on your system. The OS doesn’t care: it will give it access to everything your user has access to, but won’t give access to anything else.
So (under the caveat below) the software won’t be able to mess with your system because your user generally can’t mess with your system. However, you still need to trust the software, since it will be able to access e.g. your saved passwords, SSH keys, install a keylogger, etc. In comparison, the binary packages can be seen as safer, because they have more “eyes” on them, and there is more time between the code being published and you running that code on your system.
Caveat: if you run something like
sudo make install, then, of course the risk is way higher, and the package definitely will be able to mess with your system up to and including destroying it.