It depends on the age of your computer. Before 2003, I didn’t have much luck with dual displays because the video cards I could afford did not have good power or speed. In 2003, I purchased an HP that worked great until the mother board died this year.
I love 2 monitors and I have never regretted the purchase. They are especially great for video and comparing this when working. I was able to do similar work with one monitor, but if you do color correction or other kinds of work that involve comparing visuals, then dual monitor setups are the way to go if you can afford the price and real estate.