As someone who records,programs and produces music everyday in my project studio at home,I use a pc which is loaded with cubase sx3 and various vst plugins and instruments and I know the importance of having everything working reliably.
Whichever sound card/audio interface you use,at some point you will inevitably run into a situation where something will go wrong with your audio hardware just when you need it the most.
Possibly the drivers will corrupt which is very common,or maybe you install a new piece of hardware and its sharing the same IRQ as your sound card and any number of other scenario's.If you've got a paying client in your recording space then trust that they're not going to be very understanding when you spend two hours or more trying to fix your sound card which has decided to malfunction at that moment.
For example about a month ago I was working on backing tracks for a client which had to be finished the next day,but then my main audio interface decided to pack it in right there and then without warning.I just didn't have the time to fumble around trying to fix it at that moment with all the stress which accompanies this while your in the middle of working on a project,but I knew that all I'd have to do is to switch to my backup sound card so I could keep working.
My secondary card is also a pro audio card utilizing asio drivers which are quite a necessity if you wish to achieve low latency audio and midi in just about most pc's.
Because I use a controller keyboard which transfers its midi via USB,there was no switching of midi leads between my two sound cards which can be a potential nightmare if like me you have a lot of cabling and other things hooked up at the back of the pc.So after switching sound card drivers I was back on track within a few minutes.Quite a number of people will probably think that they can just reinstall their sound card drivers and everything will be just fine,but if your sound card is anything like my main card it will have a large install routine which will take a while to complete and will probably need a reboot or two.And if like my interface it also has considerable on board dsp horsepower and utilizes its own plugins,then theres extra stuff you have to reload.
So to conclude,in my opinion do yourself and your clients a favor ?have a 'backup' sound card (preferably a pro audio card) installed in your computer ready to go just in case your main audio interface malfunctions and you don't have the time then and there to sort out it's issue's.
