They can loosen up the reigns but I'm convinced that Captains should not be allowed to look down at a checklist or FMS while taxing. If on autopilot I still have to hand the plane over to the other guy then I think its just as wise that A's do the same for checklist items, FMS and performance stuff.

Now, nobody has run off a taxiway or hit anyone while taxing but it's a good practice when we're managing several thousand pilots not to mention the smoothness of operation when verifying critical data.