1. Beautify

Finishing, including any coloring, beautifies the wood over a raw wood surface.   It adds sheen level, accentuates grain and figure, can unify coloring variances, and can add chatoyance (glimmering like a cat's eye)  It can give cheap woods appearance of a more expensive one (e.g., poplar into walnut or cherry, ebonized wood). 

 

2. Protect

Finish can protect wood from incidental damage such as liquids (water), scuffs, soiling, bacteria and in some cases UV damage.   Look at what happens to wood when left outdoors in the rain or sun.  Think of the molding around a door from the garage to the house that's never been finished -- it will be full of dirt and oils. 

 

3. Provide a cleanable surface

Again think of the garage door molding.   Ever have one of those you have to clean?   The dirt, body, and engine oils are deeply embedded and almost impossible to get rid of without some deep sanding.   I've had to work on some farm tables with minimal to no finish on them.  I always say that they're just one spilled glass of red wine or errant meatball from getting a permanent stain.

Excellent post.  Thanks for adding it.

Thank you!