I'm new to digital audio. I had a crappy Compaq computer before that I would never have even tried to record anything on. My old "sound card" was an analog Yamaha 4-track ... I still love that machine -- always worked and allows for a surprising amount of flexibility and creativity.
But with my new setup, detailed in a previous message, I can do MUCH, MUCH more. Need to add some synth strings? Just create another track and plug in some melody or harmony MIDI notes on the virtual keyboard. Want to fatten up your guitar and vocals? Copy the best take into a new track, shift it a few milliseconds off beat and presto, you've got a wall of sound. Need to punch in and out to fix a flubbed vocal or solo? Just pre-program the exact punch in & out time, rock through the new take, and the fix magically appears. (This with Home Studio XL from Cakewalk, which I bought for $130. If you don't do any MIDI, which I didn't until I got this new setup, then you can get Guitar Tracks Pro for cheaper. Or whatever software you want, of course.)
I'm still learning my new system ... but I've got one little practice song with 13 tracks ... all played back without crackling or popping. (This at 16-bit, 44.1 khz quality ... which to my ear sounds as good as my old 4-track.)
The Terratec has been great. I chose a PCI interface because my understanding is that all the USB cards are designed with USB 1 (the old standard) in mind and I'm guessing a new generation of USB 2.0 capable audio interfaces will hit the market eventually. PCI allows for a wider "pipe" into your computer than the old-version USB portal. I like some of the USB boxes (which are portable, if you need that capability, and allow you to place the interface further from the computer) ... but the technology issue was a concern. FYI -- I have had no problem with the sound card picking up sound from the computer. I suppose it could happen if you're doing very delicate
acoustic guitar into a mic, but even then you could just set up further away from the computer and walk over to the keyboard to start & stop recording.
So, is it worth it? Assuming you have a decent home computer, it's $250 for the soundcard, $130 for Home Studio XL ... that's less than $400 for a 24-bit 96 khz capable system that allows you to make high-quality recordings & then mix them down to CD ... That's pretty amazing, considering what a self-contained DAW cost a few years back.