For most people it probably is. Ten years ago you had to buy a sound card if you wanted to play audio on your PC but once motherboard makers started putting audio chips on their motherboards, these integrated solutions like AC97 aren't flawless but for most users they are more than enough. So is there still a big market for sound cards? Extreme Tech offers their thoughts:
From my perspective, motherboard audio had some key problems: it ate up CPU cycles, was noisy, and the software supplied with most motherboard audio solutions was buggy. Anyone who's wrestled with problems caused by Realtek codecs know exactly what I mean.
In the past couple of years, though, integrated audio has improved by leaps and bounds. Being host-based, the codec makers continued to add features by writing better, more robust and more efficient software. Even Realtek's drivers and software have gotten more stable. The current gold standard, however, seems to be Analog Devices AD 1988B codec, which shows up on a lot of the higher end, enthusiast class motherboards.