I always use S/PDIF to record my Yamaha synth, bypassing its somewhat noisy analog path. Unfortunately, without a hub or combiner it's too much hassle to get back there and plug other things in, so other, less-used S/PDIF-enabled devices remain analog.
Caveat #1: if you don't set your interface's clock source to S/PDIF, you may get clicks in the recording.
Caveat #2: if you set the clock source to S/PDIF and your S/PDIF device isn't turned on, SONAR will hang on startup.