Followers, they are one of the determining factors on how many re-pins, views, comments or how much response you get for your pinned images! If your pinboard have a lot of followers, then images pinned by you will reach a wide audience. It's like if someone follow you on Pinterest, he/she will be getting all the updates regarding your activity and he/she might like your images and re-pin them which will further broadcast your image to his followers and so on! So you can see the power of having a large number of followers!