What Mac OS are you running on all of these? And why 4 computers? I find literally no need for 2 computers (unless we're talking desktop and laptop).
I'm not the OP, but....many people enjoy computers the same way other's enjoy cars or planes, or....anything. Different computers do different things, for different reasons. I use three computers (two PPC macs, one PC running Linux) regularly, and enjoy using all three for different reasons. If I had to pick one only, it'd be the Dell running LinuxMint. It's just so....tight.