Engobes are incredibly versatile and can be used in your work for a variety of reasons. The main reason is to give your work a depth of color and the variety that can be created with this type of glaze. Engobes and slips tend not to have as much movement on the pot when firing, so they’re the most effective way to color your pot if you are using intricate detailed designs and patterns, particularly if you’re using several different colors. Engobes can be used to give a pot greater depth and visual range in its decorated surface.
Engobes and slips stick together well because they both made up of a clay body. You should, however, still make sure your work is dried to roughly leather hard before coating it with your slip or engobe and putting it in the kiln.
If you only want to do a single firing, then you must use slips or engobes, as glaze must be put onto a piece of work that has already been bisque fired. You can fire them again with a clear glaze after, which will seal in your design and give the pot a lovely glossy finish.