Yes, lubrication. And did you know that back in the early '80s Toyota (and probably some others) started using Dexron II in their manual trannys on front wheel drive cars ??
Better MPG, and shifting.
Also, Dexron III (what you get today) is a very safe and good engine block cleaner. Just put a qt into your oil before you change the oil & filter. Run the engine for at least 15 minutes, and up to a few miles.
You don't need to do this but once a year, as the good motor oil we all use has lots of detergents in it.
It will clean out a lot of crap, but not every little bit. You don't want to clean out every bit, like with some of those strong block cleaners (unless you are fixing to rebuild the engine and want it super clean).
You don't want to remove all of the varnish that has built up in the bearings and such, because you will open up the clearances, and can actually cause rod knocks, and rings that will let oil into the combustion chambers, and smoking, etc.