Some snacks may be low calories as well as not containing many nutrients to keep you feeling satisfied like fiber and protein. Many snacks based on grain fall into this category, including pretzels. Pretzels are not the most nutrient dense snack.
Pretzels are defined by whatever extra flavor and dips they have that accompany them. For example, pretzels which are flavored with cinnamon or sugar that are generally called the sweet varieties, are bad for health, as are those pretzels that come with savory dips like honey mustard and even barbecue dips. Pretzels are already very high in carbs, sodium and calories, so adding on extra flavor by way of sweetening or serving them with additional dipping sauces is just going to exacerbate the problem of unhealthy pretzels.
In fact, the nutritional value of eating pretzels is basically none, as they have no nutrients or any vitamins that are good for you. You are eating pretzels only for their taste.