We should have a separate thread to debate whether using a watch (as opposed to the pool clock) is beneficial in swimming. Hard core swim coaches will be adamantly against using a watch. Tri-geeks who do most of their training on their own (as opposed to with a swim club) will usually be pro-watch (unless they come from a swim background).
I have a Garmin 910xt which I use for most of my solo swims (unless I forget it ), but I wouldn't necessarily use it in a group. I love that it counts my laps for me to track distance (it can sense when you turn around at the wall), and it even keeps track of which stroke I do. The 910xt doesn't have a "drill mode" so it doesn't count properly if I do drills-- the newer Garmin watches have a drill mode. I have used the pace clock when I forget my watch, and that's fine but it's harder to keep track of my progress. Also, since I am a pretty slow swimmer, if I lose track of how many laps I have done in a set it can get confusing (it takes me over a minute to do 50m, so if I do 150 instead of 100 I can be confused if the clock says :15-- was I really that fast? or did I do an extra lap and was I just slow...or did I go on the yellow and not the red? or did I go on the :30-- now I can't remember... hmmmm...)
I can see how it would be annoying for people to use their own watches when swimming in a coached swim with a group. But for myself I don't think I need to be a purist and insist on using the pace clock.
I can't see why one or the other can be seen as better or worse for training-- either one is a tool that helps you progress if you use it properly. I am finding having the Garmin makes my workouts more enjoyable and I'm more likely to want to do them.