There's nothing wrong with using smaller displays. I personally, despite having several modern 24", find myself more comfortable using 17"-er with my Mini.
Unlike in the old days, where 17" Apple's Trinitron was my main display and PM9600 or G4 DA were my main drivers and I had icons on the desktop in two layers on top of each other, I simply do not have enough stuff to put on a 24" real estate anymore.
Sure, some audio editors/sequencers will profit from larger screens, but even then I find that old Cubase looks a bit odd on a big screen.
On the negative side, when using older displays, one might encounter:
1. Fading CCFL backlight that also changes in color.
2. Not so optimal viewing angles of TN panels.
3. Slow response times