I used to record bass/drum tracks into a loop station which was mounted in my pedalboard. I would play the tracks through my bass amp while playing guitar through my guitar amp. I would typically have live keys and a sax player with me and this generally worked out fine. Since I don't do "live" looping, the loop station was just a convenient way to playback tracks and control them with my feet. However, I found this to be limiting for a variety of reasons.
So I've spent the last few months looking for a software based solution to replace the loop station and not break the bank. Here's what I came up with:
1) I use Audacity to record into. It's free.
2) I needed a better sound card so I Bought a Sabrent external card for $30 (CND) from Tiger Direct.
3) I use a 1/4"-1/8" mono adapter to plug instruments in for recording, or to connect the Line Out of the sound card to my bass amp. The adapter was a couple of bucks at Future Shop.
4) I control my laptop in it's entirety using The Pok made by X-Tempo. You can check out the details here:
The Pok by X-Tempo
The only other piece of software that I use is a freeware program called Vistaswitcher. Once I have all my backing tracks open, I use it to select which track I want to play. I use The Pok to control it as well. Here's a screen shot:
In addition to the above, I picked up a used Radial Big Shot amp switcher (around $30) which is mounted in my pedalboard. I use it in reverse so that I can plug both my guitar and laptop into it, and then out to my Cube 60. Just like you would do with a loop station.
In direct answer to your question, the only time I plug directly into my laptop is to record. Live playing is though two amps although I could plug my guitar into the Sabrent sound card (laptop) directly and go direct out of my laptop to a PA for example.
The Pok has been a fantastic investment and about the same price as a Boss RC-30 or Jamman Stereo.
Just some food for thought.