You want a quiet pc in the studio environment to make mixing easier.
Nothing worse than a noisy fan or something rubbing it causing weird high pitched frequencies which can make mixing a nightmare.
The longer you have a noisy pc, the less you notice it, but it will often show in your mixes....as least, that is in my experience.
My old studio pc made different noises at differing pitches depending on the workload, sometimes I was attempting to eq out stuff that wasn't there, at least, not in the instrumentation, it was the odd sounds from the fans.