Screen Size Matters!
For two primary reasons: First, the larger the screen, the brighter the projector needs to be to properly fill it with a sufficiently bright image to fully enjoy the movies, sports, games, or other content you enjoy. The rule of squares applies. A 100" diagonal screen with a 1000 lumen projector will be as bright as a 150" inch diagonal screen, with a 2250 lumen projector simplified: 1x1 = 1 1.5*1.5 = 2.25. Similarly a projector projecting onto an 80" diagonal projector with 640 lumens is as bright as a a 100" diagonal screen being hit by 1000 lumens.
The second reason relates to projector placement. You need to choose a projector that can be placed where it has to be to fill the size screen you would prefer. It's quite possible (especially with the projectors with rather limited range zoom lenses), that in your room, you might find that you can place the projector nicely to fill a 90 to a 110" screen, but not anything larger, because perhaps: The room isn't deep enough to place the projector far enough back to fill a 120" screen, or perhaps you room has a limited places it can have a projector installed. A 90 – 100" might work, and then a 115 to 133" might also work, but you have a wide soffet where you can't mount the projector, that "take's out, that 100" – 110" screen. Of course if your room has few limitations, and the projector is flexible, then almost any size can work – given that the projector is bright enough to fill that screen.