Most people who care about language and good writing would probably tell you to avoid foul language and swearing, and with good reason. Just because you riddle a text with curse-words (or "cuss-words", though I've never been a fan of that expression) doesn't make it interesting or edgy. Well, edgy in the sense that your sure to offend someone, but no amount of cursing can bring an edge to dull content (though it's often tried).
But cursing, when used in moderation, can often add some spice, and maybe even stilistic contrasts, with swearing. Think about a generic rap-song, or just about any Quentin Tarantino-movie, where it seems as if every other word is a curse word. In that context, where the listener is flooded with swearing, the curse word loses much of its weight. If you try to make anything stand out using a curse word in that situation it would be like dropping a teacup while the elephant is rummaging the porcelain-store; nobody would pay much attention. But imagine if the suburbian next-door mother of 2.5 children would suddenly start cursing like a sailor? Wouldn't that raise an eyebrow or two?
It's all up to what you want to say, and how you want to say it. Even though we cannot emphasize our tone of voice on paper, we can still use words of varying gravitas to fit the situation, and better express the mood we want to create in the reader.