Porous surfaces should be primed with acrylic white gesso. I prefer to prime almost all surfaces with at least one coating of this to give a controlled white painting surface. For very large paintings, such as murals, it is very acceptable to paint right on a clean dry plaster. Unlike oil paint, they will not harm the fabric, so no previous preparation is necessary. Sizing a fabric before painting will keep the amount of paint absorbed to a minimum, and therefore control bleeding and the amount of paint used.
Acrylics are very good for painting on clothing for costumes.
When it dries, the paint remains very pliable. Because of its pliable nature, ease of use, and the fact that it is water-based, acrylics are the backbone of theatre set painting. There are complete lines of paint made for this very purpose and companies dedicated to their production. They can be used on any other form of paper also. It is a good idea to prime any heavy paper which will have thick paint applied to it just to keep it from buckling.