It all depends on what you are doing with it. I couldn't imagine bringing a desktop into a RV. We usually travel with just 2 laptops, but when we are at our seasonal site, we all bring a laptop.
Desktop's still have their place in our house, but most of us use laptops. I am an independent web site developer. I have a high-end 17" gaming laptop with 2 24" 1080p HD monitors and I use the 17" screen for a total of 3 displays. When we travel, I take one of the monitors with me. We love to have them both, but there just isn't that much room in our MH.
And yes, I use my 17" laptop on my lap when I'm not working and connected to the 2 monitors.
-Michael