Many people have focused on what fast-paced can mean but I think there's one other reason: many shops are slow-paced to the point of stagnation - picture the kind of place where finding a problem results in either requesting off-site training or filing a ticket and going home for the day. If you're hiring, there's a desire to avoid submissions from the kinds of developers who got into the industry thinking "indoor job, no heavy lifting" but this particular wording is too cliched to actually do that.