(i) it’s generally much faster to get out more ideas,
(ii) people generally respond more positively to something hand-drawn; they get to see more of each others’ characters come through, and it’s always more dynamic and interesting than something produced digitally
(iii) it’s a better way to deal with varying degrees of confidence in ability; using paper templates, smilies and markers is more forgiving than digital

I remember a while ago using GoToMeeting for online drawing within teleconferences (http://www.gotomeeting.com). To be honest it was a little clunky, but it got the main ideas through to everyone, and allowed everyone equal access to add their parts visually.

But most of the times I’ve used storyboarding within a workshop is for everyone to do their own storyboard to illustrate their own experience. In these cases, what they produce really isn’t up for others to modify, but to read it and promote discussion and further ideas.

Using digital tools for other collaborative design efforts, though – like interfaces – is a different story!