Need more screen real estate but can't stand the clutter of an additional monitor? Funds spent on a modern monitor are about as high-impact as you can get. Now you'll be able to use even MORE tabs in your favorite browser, research while writing, or play games the way they're meant to be played - all on a single screen.
Bezels have gotten smaller and panels have gotten brighter over time. If you're still toughing it out on a $100 monitor from a few years ago, you may be able to appreciate the brightness and quality of something newer and (maybe?) larger.