Whether a new mama plans on breastfeeding or not, she will almost always start to produce colostrum (the pre–milk liquid) and then breast–milk a couple days later. When it starts to come in, it's nice to be prepared.
I was lucky as a close friend of mine warned me about soaking through shirts and gave me nursing pads as part of my shower gift. During my eight months of nursing, I purchased cases of these suckers, I mean soakers. And they were worth every penny. I never had an embarrassing moment of leaking through a shirt in public.
I tried both disposable and reusable pads and preferred the disposable ones as I thought they kept better shape and were more sanitary. But I also have friends who swore by the washable ones.