Can someone please explain to me what the purpose of bushing is in a motor and what would happen if it was not present?
Some people call plain bearings bushings
The etymology can be different based upon geography.
If you have a 'bushing' in your engine it can commonly refer to a crankshaft plain bearing or a connecting rod plan bearing.
Here is the wiki on 'bushing'.
A plain bearing that is missing out of an engine would be unusual. To remove a crankshaft plain bearing an engine would have to be torn down, the same goes for connecting rods. Sometimes these bearing can be accessed from the bottom of the motor via removal of the oil pan at the bottom of the motor.
The purpose of a plain bearing is to reduce space between the crankshaft and the engine crankcase so that lubrication can be delivered to this area and the crankshaft. The crankshaft would float on a cushion of oil between the crankshaft and the plain bearing. If there is metal to metal contact the engine will destroy itself.
I hope this provides a viable explanation to your question.