While many people mount their projectors, fear not, plenty of folks (maybe including you) need flexibility. Maybe you want to use your projector in more than one room? Or more typically, perhaps you only have one room in mind, but on some occasions, it leaves the room? You might take it to your summer cabin, or more likely if you have a family, it might end up in the backyard for summer movie nights (or project onto your garage door).
For the small business person, it might help to have your projector double for business use, perhaps for an occasional presentation. If any of those things seem likely, then you will have multiple rooms to deal with. Some projectors are just more versatile, and thus better suited for you. Not so much the over $2000 projectors, but definitely for many from under $2000 to well under $1000.
Bright projectors, of course provide more versatility. Built-in decent sound that is great if you want to move it around, although there's no substitute for a good surround sound system. If you have business projector needs, there are projectors with some very good image quality for home while doubling for business. Consider your portable needs, but otherwise look to match your projector to the room that you will primarily use.
Here, a temporary setup (imagine for a Super Bowl party). The screen and projector are both portable, and not permanent fixtures in this downstairs common space with large windows and light surfaces. Not as bright a projector, nor is the screen ideal for this room.