I always allow my bottles and kegs to drain well but sometimes wonder if left too long the star san sort of forms a slimy coating. I have noticed this when I have left the star san in contact with what ever I had the star san in, say a large measuring jug... takes a lot of cleaning off! I will say I have not noticed anything amiss but wanted to get a heads up. I used to use a bucket of water with metabisulphite back in the day and never had an issue but it seems these days you must use a sanitiser.
edit
I did see one homebrewing video where the American brewer actually said " don't fear the foam it is good for your yeast" is that actually true?