Over the winter I bought a Focusrite Scarlett 2i2 USB audio interface for the purpose of hooking my acoustic guitars up to my comps, which I haven't bothered to do yet. But most of what I do with music on the comp is just with VST's in daw's and sometimes plugged in to notation software like Overture. I rarely record any audio and don't plan on ever recording much audio. I kinda like keeping my acoustic universe separate from my electronic universe. I've been happily using my on board sound card exclusively for a long time. If I'm only using VST's on a project would the Focusrite improve playback quality through my speakers and/or render quality when generating mp3's compared to what I get using my on-board sound card? I know this is really basic, but, frankly, I don't know if the sole purpose of this device is to connect physical instruments, or, if it also improves these other things. Thanks in advance for any guidance.

Grr. Can't figure out how to move this to hardware forum.

Solved.

Hook your headphones to it and use it as you default audio output device. That'd be the best way to compare it against your on-board audio device.

An external sound card will let you use ASIO drivers where the factory card usually will not. 

The sound quality should be the same in both BUT.... the big advantage to an external interface is with the ASIO drives and especially in the area of performance. Lower latency and smoother operation is the big difference. 

I would use, and do use, the external for everything related to Cakewalk and other music programs. 

You can you ASIO4ALL drivers with your built in sound card. I would say that a dedicated audio interface can't hurt playback and will be better for recording at lower latencies should you decide to record audio.