The straps are for positioning and holding the cups in place. It's primarily the band that supports everything. It's a mistake a lot of women make. If the band is too loose (which it will be if you follow most manufacturers' directions for measuring, plus the cups will be too small), you'll end up with shoulder pain and backaches, because the weight will be unevenly distributed and you'll tend to slump forward. For example, following most manufacturer's measuring directions, I'd wear a 36 band size. After being professionally fitted, I know that I wear a 32 band size and when I buy the right size (and shape, that's important, too, and very individual), I don't get back or shoulder pain and the bras are usually quite comfortable.