No. The Booster (a mixture of corn sugars and dextrins) is an optional product. It will boost the alcohol by approximately 1.3%, but it is not required.
Our HME's (hopped malt extracts) contain all the fermentable sugars necessary to create your beer. An all-malt beer will always have fuller flavor and mouthfeel than one using non-malt adjuncts, such as corn or cane sugar, which can thin the body and dry the flavor profile. We don't recommend adding booster if you want a full-flavored beer, but rather a BrewMax SoftPack LME (Liquid Malt Extract) or DME (Dry Malt Extract) to raise the alcohol % of your beer and provide more flavor and body. But Booster is great for lighter bodied beers when you want a little more kick.
Our Standard Refills come with booster at no extra charge, but it is not required to make your beer. Our Deluxe Refills come with a Softpack LME.
For some styles Booster is appropriate so there will be recipes where you see it used. Each refill/recipe on our website has instructions in the product details. Please let us know if you have any further questions.