I use it any time I need to capture audio 3/4. It has the ability to capture Video + audio 1/2 into an AVI file while simultaneously capturing audio 3/4 into a separate WAV file. It works great for its designed purpose.
I use it as my main capture program. I tend to shoot lots of very short clips (15 seconds to a couple of minutes at most). The index that Scenalyzer creates is great for helping me find what's on a tape and capturing just those pieces.
I use it 100% of the time. What I particularly appreciate is that ScenalyzerLive uses the date/time stamp as the name of the avi files it captures. This uniquely identifies them as well as identifying the order of shooting. The software user interface is a bit unconventional, but it works. I don't use the "5-minute" capture feature, but perhaps in the future I will see how it can be useful.
No codec is involved in the capture - it is a straight digital copy. Scenalyzer just adds the AVI wrapper. When you then use it in Vegas, and transitions or effects will use the Sonic Foundry codec.