I think snacks can be a useful addition to toddler nutrition. They can't eat enough at meals to fulfil their calorific needs. I suppose its a bit harder with older kids.
I don't give sweeties or chocolate. I tend to see raisins as sweeties really, and limit those. I am very wary of ds' blood sugar (I have real problems with mine esp when pg/bf) and keep him on a low gi (but high calorie) diet, ie lots of dairy.
I am a complete food fascist about stuff like ice-cream, chocolate etc. Ds has those maybe once a month, if that. But oatcakes, cheese, milk-he can have those whenever he likes. He's certainly got enough energy!
But I am a smug mummy because ds will eat garlic, chilli, and, as of last week (gasp) lettuce.