Every word has a place in communication, and each word should be used accordingly. Swearing is an accentuation to a phrase, or can be used to indicate a harshness of tone.
Example (accentuation):
1. "This game was awesome!"
2. "This game was fucking awesome!"
The tone changes as you read the examples. It is clearly demonstrated in Example 2 that the speaker felt strong, positive emotions about the game, whereas is Example 1 the speaker simply expressed a strong like, or approval of the game.
Example (harshness of tone):
1. "You're worthless."
2. "You're a piece of shit."
Note the difference of mental images that the two phrases generate. In Example 1, the idea is presented that the speaker believes the individual to whom he is speaking to not be of any value, which is in itself harmful, but it gives an intangible concept. In Example 2, the speaker expresses the same sentiment as in Example 1, but this time gives the tangible concept of excrement to indicate his feelings towards the individual. Example 2 gives us a better understanding of the sentiment, due to the mental image it brings.
Profanity is not needed to express sentiment or emotion, but it is a powerful tool in doing so. But like any device, its overuse will dull the effects of the words and their connotations, thus dulling the sentiment altogether.