When a chain becomes dirty, dirt is spread to other parts of the bike. This could mean having to replace other components—which can be expensive.
Important note: Cleaning your chain too often could remove the original lubricants that your bike chain was built with. Replacing this can be very difficult so try to be careful.
Over time, water can seep between the saddle post and frame of a bicycle. If left untreated, this causes corrosion that makes it difficult to remove the seat from its base.
Due to the face your pedals get very close to the ground, they can pick up dirt very easily which means they need to be cleaned as well as re-greased on a regular basis.
If your bike has external cabling you will see that underneath your bike is a cable for the rear brakes and the deraillers run through a guide.
If water get into the housing of your brake cables, it can cause it to rust and fray. If you regularly apply lube to the cable, it can prevent damage happening.