Understanding the workings of a washing machine is not rocket science. It is simple and easy but if not kept in mind, could damage the machine.
1) Washing drum
Due to overloading, the drum will lose its balance. This will not let the drum spin freely and will instead tumble over the walls of the machine.
Overloading will result in lack of breathing space for the clothes to wash properly and your dirty laundry will remain dirty. The detergent will not be washed from the fabric and due to the low speed of the cycle, the clothes will not dry completely.
The residue will be stuck on the walls and the clothes. The load will come out smelling worse.
So, always make sure you do not overload the machine.