It should be fairly obvious that if you're playing a fast fiddle tune, you either have to slur lots of notes or use separate bows, and at the speed you'll have to go, you won't have time for the whole bow for each note. I don't claim to be an expert at any kind of fiddle playing, but I'd think it's better in general to use lots of separate bows, rather than slur the notes--unless in a air, waltz, or something similar. I actually far prefer the airs, waltzes etc.--but that's a separate issue.