One of the things that has annoyed me (way beyond annoyed - but that language is not allowed here) about the potlucks I have gone to - the people that put a mountain of food on their plate - and then discard it -
And if one is one of the last tables to get in line - one is lucky if there is pickle juice left and scrapings from the casserole dishes.
I see no reason to take more than a dab of food that one is unsure of - and to not take any if one is sure one is not going to eat it.