Often it is important in an illustration to tell a story in the most simple way, by means of a cut away, cross section or an exploded view. Keeping the focal point on what is really important and minimising the unnecessary information.
Land form cross section
Pavlov's Dog experiment
Car Battery Cutaway
Home Water Supply
Arm movement
Fielders Mobile Mill
Braemar Gas Ducting
Sectional cutaway of Sand Blaster helmet