My kids never had to ask for snacks for themselves at home. Occasionally, i might see them reaching for a bag of chips and ask him to wait until dinner. If they were entertaining guests, they would ask what they could offer their guests if we were around but if we weren't they knew what was appropriate to offer.
As guests they were taught to not ask for snacks unless offered.
I do have friends who required their kids ask permission before eating any snack because they wanted to more closely monitor their kids food intake. Some times it was because of dietary restrictions but lots of times it was because if sweets or snacks were around their kids would fill up on them and not eat at meals. I understand their desire to still have treats in the house while teaching their kids some self control by giving out a portion or redirecting to something more healthy to take the hunger edge off without spoiling dinner time. I also had a friend who's daughter showed early signs of being a boredom eater so requiring her to ask for snacks helped combat that problem.