It depends on your need(s).
I'm more into music, amps and instruments, and music software. So my point of view would definitely be subjective. But bear in mind that most of the newer or latest motherboards have integrated audio that are very decent. Some integrated audio are now coming as 7.1 audio.
However, if you're into recording from external sources into your computer, than a dedicated sound card is the way to go. (And even then, there is the on-going issue of crappy sound cards, decent sound cards, excellent sound cards, and exclusive high-end sound cards used by some recording studios that cost over $3000.00).
Also, most diehard gamers and other multi-media enthusiasts invariably use top of the line sound cards in order to get that "feel" of being in the game, or in the movie, or in the orchestra as per sorround sound and etc.
So most integrated audio nowadays can do a pretty decent job of giving good sound. But another can of worms is having integrated audio ar a very expensive sound card being played through crappy speakers. That's another issue, altogether.