Oil and oil finishes should not be built up on the surface of the wood because the cure too soft.
Therefore, they can't protect by forming a thick film, as other finishes do between the wood and the surrounding environment.
Any protection oil and oil finishes provide has to be either in the wood or very thin on the surface of the wood.
In fact, it is a little of each, and both are necessary to achieve maximum protection.
Oil and oil finishes don't provide much protection against water vapor exchange.
But what little protection they provide comes from the finish that penetrates the wood.
A barrier forms just below the surface, which slows the exchange of water vapor and thus reduce swelling and shrinking.
The finish that remains on the surface of the wood provide limited protection against stains, water damage (smudges), and abrasion.
Straight oil soaks into the wood much more deeply than oil blends because straight oil takes much longer to cure.
But oil blends usually form a better surface barrier because of the added oil.
Neither finish provides very much protection against abrasion or water damage, because they are so soft and thin.
It is therefore important that you maintain the integrity of the surface film by re-coating it anytime it becomes scratched, worn, or dull.
To achieve the best protection with an oil blend, you have to create continuous film, one with no voids.
The best way to do this is to apply the first couple of coats very wet and let the soak in for at least five minutes before wiping them off.
The heavy, wet cat will allow the finish time to penetrate and form an internal barrier against water vapor exchange.
It will also stop up the larger pores so a continuous film can form over them.