Image what "This piece of software is fucking useless" would sound like if it was read out by Stephen Hawking's speech yoke, 'fuck' doesn't emphasize anything, the inflections and tone of your voice do. A charismatic person could convey far more emotion by dramatically saying "This piece of software...it's useless! It's...useless!!" than a dull person who says 'fuck' with a monotone voice would.

It adds nothing.