I myself take 3 protein shakes a day in addition to 5 solid food meals. Some at Breakfast, Before training and after, then a slow release before bed. However, nothing replaces solid food and lots of it. Milk is a great way to also get additional protein at every meal.
ALSO, even if you are using this between your meals, those snacks should be around the same caloric ratio as your meals. Get at least your body weight in protein every day.