When you're starting out making music having just one computer for everything is fine but once you've reached the point where you spend a lot of your time on it, it quickly becomes a no brainer to at least have a dedicated computer for just that. It's about putting yourself in a productive setting where you only focus on creating and you have minimal distractions.

Besides, a dedicated computer for music production has a low entry cost since you basically only need a decent amount of ram. My studio computer has an old i7, 32 GB ram and it doesn't even have a GPU and the price was less than $500 a few years ago. It's going to outlast my current gaming rig and probably my next one as well.