Reducing friction in engines relates to extending the life of the engine. It also relates to squeezing out maximum efficiency from the operating system.
Don't be fooled - the lubricating systems in cars and trucks today are admittedly pretty good at doing their jobs. Anyone who claims otherwise is overselling their claims. If you don't use an "oil additive", your car isn't likely to break down any time soon from lack of lubrication.
That being said, there is room for improvement in certain areas of performance.
Unless you are using an oil that specifically says otherwise, you're pretty much guaranteed that the multi-weight oil you buy (such as 10W30 or 5W20) comes with an additive package already contained. These additives function to better protect the engine beyond the basic lubricating function that the base oil fulfills. Contaminant dispersants and acid neutralization are basic functions of this package.
Of course, these additives have a limited capacity to do this job. That's why waiting too long to change your oil is so bad for your engine.