A lubricant has many functions aside from lubrication. Industrial lubricants are formulated to attain certain properties that makes them suitable for certain applications. Some are designed to handle intense heat while others are formulated to not coagulate when exposed to very low temperatures. Other lubricants offer high resistance to corrosion while others are designed for handling high loads.
A lubricant can also be used for cleaning items around the house or workplace. The typical all purpose lubricating oil have the properties that make them sufficient for cleaning chores. Lubricants work especially well for cleaning and protecting metal items.
Moisture is one of the greatest enemy of metals. It causes rusting or corrosion which damages metal the surfaces of components. If left unattended, the corrosion can get into so deep that the structural integrity of the metal object is compromised.
Regular wiping or brushing of oil on metal items helps protect against moisture and removes unsightly rust. The oil layer creates a barrier against air and moisture thereby preventing the metal surface from reacting with it. In the case of rusting, the oil sips into the deepest layer and helps loosen the rust buildup, making it easier to remove.
Some people mistakenly believe that protective coating processes are able to provide enough protection to metal. There are indeed coatings that are designed to protect metals from corrosion. Black oxide coating and chrome plating are two of the most commonly used methods for protecting metals. However, even these methods are not able to provide complete protection against damages caused by moisture. If you look at chrome surfaces, you will see minor signs of corrosion. This is mainly because chrome plating is often applied thinly as thicker plating is more prone to chipping.
As mentioned, the only way to protect and preserve metal item is regularly cleaning and applying protective coating. A lubricant can do this two tasks.