Projecting up or down isn’t necessarely problematic but something that often needs more consideration than projecting horizontally onto a screen or wall. Many projectors are not “safe” to be used if inclined more than 15° as it can upset their cooling and airflow.
With more demands for projecting vertically though, many manufactures are designing projectors to be able to cope with this situation. It’s worth noting though that there may be changes that need making to the settings so as to avoid damage to the projector.
Rigging is ofter a problem too as typical hanging brackets are simply not designed for this purpose. Should you want to use a projector that is not designed to be used vertically, an optical projection mirror can be used to bounce the image up or down. If you have a vertical projection requiemt, please get in touch and we will advise upon a sutable solution.