Metal Protecting !

ANY petroleum oil will eventually evaporate. The higher the viscosity, the slower the evaporation rate. This is why WD-40 sucks for long term storage; it r evaporates away.
Grease works well, but it's a ***** to get in threaded holes and even worse to get out, risking a damaged hole if it's a blind hole. When grease dries out, it can become a solid that does NOT like to dissolve or reconstitute.

We use cosmo in machined cast iron railroad assemblies that are never maintained and sit outside forever.

I like cosmoline because it goes on fairly thin, viscosity wise about like a heavy motor oil, but the volatile compounds rapidly evaporate and it becomes a waxy grease. It flows well when a liquid and penetrating action is relatively high. Warmed much over 120degF, and it will flow again and becomes very easy to wipe off, and it will wick and redistribute itself over the surface. Automotive grease won't flow like that, which compromises protection.
MANY firearms over 100 years old exhibit fantastic metal protection thanks to cosmoline, even after ocean shipping and poor storage conditions.

You'll understand the penetrating ability after you get it in your clothes or on your skin. Rust-veto 342 is the modern name for the old US cosmo. We also use one of their lighter preservatives that can be sprayed in with a regular spray bottle. When it dries, it looks like nothing is in the surface, but if you touch it, it melts into oil again, just from your body heat.

Old guns packed with grease can seize up due to the grease getting rock hard. Cosmo gets sticky, but not hard. Cleans up with gasoline, or elbow grease, lasts DECADES.