There’s something comforting about large screens; I’m well aware of that, and I feel it too. The expanse of screen-space hints at creative possibilities. You probably wouldn’t want to do full-time graphics work or app development without a large and/or additional screen, either. You can, but those are specialised disciplines where you can make a strong argument for two-up or even larger displays.
For the vast bulk of stuff that most people will want to do on a computer, though, most of the time you don’t need a desktop monster. I don’t think you even need a 15” screen, which is essentially a portable desktop. You just have to use a small screen productively.
Dear Macbook Air user, you should read this.