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.
Pavlov's Dog experiment
Braemar Gas Ducting
Sectional cutaway of Sand Blaster helmet
Land form cross section
Home Water Supply
Arm movement
Fielders Mobile Mill
Car Battery Cutaway