On board sound vs dedicated sound card
In the old days of motherboards didn't have built in sound video and network cards but over the last ten to fifteen years, these components have been integrated into both motherboards and processors. Motherboards used to come with several expansion slots to accommodate these components but now, some motherboards only have a couple of expansion slots and some don't even have a pci slot at all. Sound cards used to be discrete components but are now integrated into the PC's motherboard. The trend towards integration has all but killed the market for sound cards, but there's still a small market for high-end cards that promise better sound quality relative to integrated alternatives.
The function of a sound card is to produce sound and expanding audio output. Audio is not as demanding as video since there is less information involved, but does that mean the task is trivial? Audio does use some processor cycles, so off-loading it to a dedicated chip may be preferable. But since most motherboards now have a chip on-board, are dedicated sound cards worth the extra cost? A more advanced audio chip may also include hardware that enables features like virtual surround sound, a pre-amp, or niche audio formats. Almost all motherboards, no matter the on-board audio used, offer no better than 5.1 audio via standard 3.5mm jacks. Some don’t even manage that. A sound card is usually required to make a PC compatible with 7.1 audio and common home theater outputs like S/PDIF.
Sound Quality
Sound quality is mostly subjective so it is difficult to measure sound quality. There are standard but reviewers generally don’t have the necessary equipment used by manufacturers to calibrate premium audio hardware. Measuring the difference between sound usually requires blind comparison tests and are also difficult since auditory memory is very short. There are some that still run these types of test such as The Tech Report. The Tech Report have tested several dedicated sounds cards over the years using a combination of testing hardware and blind listening tests to determine the quality and found that there are noticeable differences in audio quality. But the difference in audio quality can be hard to notice in games. There are two reasons for this. First, games often focus on visuals rather than sound, which means players usually can't concentrate on the audio. Games usually don't have high-quality audio.
Surround mode
Improved surround sound on dedicated sound cards may benefit some games that incorporate surround sound. Some games have surround-sound modes that only work with hardware audio, and some audio cards have virtual surround sound modes designed to improve the quality of the sound. Both can lead to a more immersive experience. You should remember that headphones or speakers have a bigger impact on the quality of the audio. If the sound card is connected to a 2.1 audio system, your audio system won't be able to produce a noticeable difference.
Performance
Even though a dedicated sound card reduces processor load, it may not be noticeable. Integrated sound on a motherboard handles the task pretty well, and processor performance is not the limiting factor in many modern games so they may not run quicker if a sound card is installed. There isn't much of a difference in latency either ( the time it takes for audio to reach your speakers ). In some cases, a dedicated sound card may be slower because they require additional processing that an integrated chip doesn't, but again, the difference is too small to notice.
If you are mainly gaming on your pc, any difference between a dedicated sound card and the on board sound will be hard to notice, and most games don't have high fidelity audio good enough to make the hardware matter. Games also tend to focus on visuals, so there are few audio sequences where you as a player will appreciate. If the games you play feature surround sound and you have the speakers to reproduce the sound accurately, a dedicated sound card may make sense since not all on board sound chips can handle surround sound. Dedicated sound cards make the most sense if you watch movies or listen to music. In these situations a difference in quality is easier to notice and the source audio quality is pretty good. If this is your case, you may also want to hook up a premium 7.1 system or a larger subwoofer, hardware most motherboard audio can’t support.