Classic juicing will pulp the fruit or veggies and separate the juice (water) from the solids (the rinds and fiber). You end up with a glass of juice at one end, and a bucket of moist solids at the other end. Most people then throw away the solids and drink the juice. But there are many good things in the solids that you're losing.
Using a blender, the fruit or veggies are pureed and the solids and juices are mixed together very well into a smooth paste/liquid, there's no by-product. All the goodness is preserved and nothing is thrown out.
But you still have the problem of too easily consuming. This is great if you're trying to overconsume, but most people are trying to lose weight. Just eat the fruit/veggies whole, and your body will naturally tell you when you've had enough