Putty is often used to prepare a smooth, even surface prior painting. It fills in minor cracks and holes and removes any undulations on walls.
A primer is a substance that is used as a pre-coat before paint application on any surface – walls, wood or metal. Primer improves the adhesion of paint onto the surface and enhances paint durability.
Priming can be skipped if matte finish paint is used. It is always advisable to have an undercoat of primer if a gloss (sheen) finish is desired or when painting a shade way lighter or darker than existing. However, priming does not cost must and it increases the durability of paint, it is advisable to have one.