Exactly what I said, it increases the quality and clarity of the sound. Mainly due to the onboard sound processor, but also because it doesnt have other electronics right next to it that interfere with the signals, causing minor interference and such. Sound cards also usually use higher end components.What do you mean "increase the quality of sound"?
so if if you were into watching lots of movies and listening to music which demands high fidelity? is it worth buying one?
They usually do, but i've heard some Creative cards are actually known to use more of your CPU's processing power and RAM.Don't sound cards also free up some processing power?