I'm honestly not sure if one can hook up 2 20" or 24" monitors to a MacBook Pro these days, but even if you can't it's nice to have a desktop with a mouse and keyboard and not have to plug/unplug your laptop from everything all the time. Also, I prefer linux on the desktop (for my work machine, not personal) and Mac OS on the laptop, but that's just me.
I have a 30" monitor (with dual DVI) at home, and not being able to use it with my mini-DP MBP is a tragedy, let alone being able to connect a single laptop to two monitors...