When canning, it's important to bring the brine to a boil to ensure any impurities are dispensed with. When making pickles for the fridge, you don't need to boil the brine, since you'll keep the pickles under refrigeration and use them within a month. I like to heat the brine to dissolve the salt and use it when it's still fairly warm to help extract the flavors from the garlic, dill, and spices. If you feel better bringing it to a full boil before using it, you're welcome to. Just don't boil it for too long, or it will get too concentrated.