Its not always possible to stand the projector on a tripod somewhere handy, if you don't have a side kitchen or you have overhanging cupboards that get it the way. It may be that you just prefer to have an adjustable bracket that you can fix to the roof and simply screw the projector on and off as you use it. 
This bracket is perfect for the job, allowing you to adjust the projector to just the right angle, and leaving only a very small fixing to the roof when not in use so the risk of catching your head on it is much reduced.  To fix, simply find the optimum spot and attach with two small screws.