At home DD (almost 4) will have one snack mid morning and one mid afternoon. She has breakfast at 7ish, lunch 12.30 ish and dinner 5.30ish. 5+ hrs is a long time for little tummies to go without a top up.
Also it's a habit created at nursery - she has breakfast when she gets up, sometimes a piece of toast as second breakfast when she gets there, snack about 10, then lunch at 11.30, another snack about 2, tea at 3.30/3.45 then she needs supper before she goes to bed. It means she's used to that pattern of eating.
DD does get grumpy when she's hungry so she does still need it.
I expect it to drop off naturally as she gets older. Once she goes to school next year it will be breakfast, a piece of fruit mid-morning, lunch, I expect a post school snack, then a sensible dinner.
I agree the content of the snack is important though. At nursery it's either fruit or breadsticks. At home there's more variety and I flex content and size to how well meals went. When we're out and about it changes again. Meals can be off schedule, or she didn't like it and only really ate chips for lunch so a more substantial snack of veg sticks and cheese or a few peanuts is needed.
If you're thinking about it from a weaning perspective then yes, little kids do need snacks. But spaced out snacks, not food every 20 minutes!