Nowadays a lot of motherboards include audio and video. As a result, they are more expensive but there is no need to buy sound or video cards.
It is rather difficult to select between integrated sound and video expansion cards. First of all, the use of a simple audio codec of AC 97 Standard leads to a significant worsening of a sound palette even in comparison with the outdated sound cards for ISA-bus. Besides, audio processing is handled by a processor. So, the purchase of a motherboard with built-in dual-channel (2.0 Index) codec AC 97 is warranted only by its budget construction. But if you have separate sound, you must switch off you built-in s audio codec. To switch it off, select the value “Disable” for the parameter “AC 97 Audio” in a section “Integrated Peripherals” in BIOS Settings.
From the other side, a lot of manufacturers produce their motherboards with built-in codec or even sound processors of good quality. For example, a codec Analog Device which is used in chipsets by Intel, or DSP (Digital Signal Processor) which is used in chipsets by nVidea. Thus, one motherboard has got five- or six-channel sound card (4.1 or 5.1 Indexes accordingly). Of course, if you have such motherboard, there is no need to use a separate expansion card.
If you use cheap simple speakers, the choice between a built-in codec and sound card makes almost no difference in the sound quality. The better sound, the better your speakers should be and the higher requirements should be applied to audio codec and sound card.