There are and were all kinds of competitions. The wild category is probably the most obvious one regarding no size limitations, but the generic "combined demo" category which is very often present at competitions is also usually without restrictions (but it must run on the competition machine).
OHP Mega Demo 9000 is one of the greatest things to come out of the scene.
Fun fact: In the famous HBO "spinning chrome logo" intro ( https://youtu.be/i1NKoMNy5bY ), the sole use of a computer in generating visual effects was to control a servomotor that slid one patterned transparency over another, much like this demo, to create a "starburst" effect (seen just before the logo itself appears).
