To be honest, for the application in GMFL's photos, he'd be far better advised to use a soft-setting absorbent Teak Oil of some kind - not a hard varnish - for all the reasons you mention.
If varnished he'd have to do it all over again in a year or two anyways.. and an oil is far easier to maintain if caulking is involved.
Sorry, I have to totally disagree with you here. This is even bordering on bad advise. While I know some people prefer the weathered teak look on all their teak (or just prefer not to maintain it). I'm not one of those. For the cockpit sole, the teak is just that and I don't plan to change it. If I had teak decks, the same would go. But this area is not used for any major foot traffic so varnish it is. Oil BTW, just attracts dirt and would need monthly cleanings and re-oiling and never looks that great IMO. Same goes with Cetol, might as well paint it if you go that route. Again, my opinion.
As for having to do this all over again in a year, well, not quite the case. Sure, if I re-varnish and don't maintain it, then that statement may be true. But properly covered and bi-annually light sanding and re-coating should give me many many years without having to re-strip the varnish.
Maybe I should have stated I'm a contractor and have experience with many a tool and actually enjoy these projects. I just haven't had to remove varnish from caulking before.
I do thank you for your opinion though.