I used a MacBook Pro as a server for years. It was fine for its purpose, however the battery did swell and need replacing. It may have damaged the trackpad, and like the other comment mentioned, idk what would have happened if I had left it swelling for a couple more years. Probably not a battery fire? But the $230 or so that a massively more powerful HP USFF that I replaced it with was worth it, even versus a 0.1% chance it would burn my house down and possibly kill my whole family in the process.

I ended up repairing the Mac, replacing the battery, and installing Chrome OS on it. (chrome sucks though, someday I’ll get it back out and switch to real Linux)