Marin and caltex,
Teak is wood from a tree. Are you two saying wood dosn't need any protection at all? ......
Depends on what the wood is being used for. If it's on a house, yes, it will benefit from protection (paint, stain, etc.)
If it's a deck surface, the intengrity of the seams and the longevity of the wood will be maxmized if you don't put anything on it at all
ASSUMING that what you want is a surface with great traction, wet or dry.
If all you want to do is maximize the life of a teak deck surface with no regard for anything else, sure, paint it. Or do a real good varnish job and then protect it from UV and the weather in a boathouse when you're not using the boat. But in both cases you'll be maximizing the longevity of the wood while sacrificing traction, particulary when it's wet.
So in my wife's and my opinions both of those kinds of protection negate the benefits of having a teak deck in the first place, which is to have a deck that gives great foot traction wet or dry. For that, you need the wood surface to be bare and clean.
So you have to pick your priorities. There's no one-answer-solves-everything other than simply not having a teak deck at all. And that's a matter of personal preference. My wife and I really like a teak-surfaced deck and we don't like a fiberglass-surfaced deck. So our priority is maximizing the life of the teak decks on our boats while still preserving the properties that make them worth having, which is traction. That means bare wood.