Sometimes for a church, they'll put the projector way at the back of the chapel, and project onto the screen up onto the stage area in the front. For those projectors, you'll need to buy the optional - shall I say - "a big zoom lens" to reach that far. Some have that accessory, some don't.
Also some places (whether in boardroom or church or hotel conference room) prefer to permanently mount the projector from the ceiling. If this is what you need then you'll have to look for a projector with ceiling mode (ie. project the image upside down). Again, some can, some can't.
Then the issue with supported resolution. Nowadays most laptops are widescreen, but not all projectors will accept such resolutions (most projectors at my work place supports only 4:3).
