Not a stupid question -
Dual monitors simply mean more work space and depending on how you work or what apps you work with, two monitors is a requirement.
For example, I use Nuendo and Sonic Foundry Vegas day in day out...I like to have my project (track view) completely covering one monitor and my mixer/effects/inputs etc on the other monitor. Once you get used to two screens - you will never go back.
One monitor can be okay but it can also lead to constant scrolling, window repositioning and extensive mousing that wastes time and generally slows down my workflow.
Pretty much anyone who is really into their work/apps/workflow go to 2 monitors ASAP. I just switched over about 3 months ago and I can tell ya - 38 inches of screen is way better than 19.
Cheers,
Cuzin B