Remember when you were having a family dinner as children and the table became congested with empty glasses, plates, cutlery and so forth? Well, it is the same situation when guests have to deal with a messy table. In many instances I see servers that don't even take the initiative to make sure that their guest's table is free from excess items. ie. empty glasses and bottles, unused cutlery, finished plates. Not only is this a lack of courteousness toward the guest but it represents a bad reflection on the establishment itself. A clean table shows that the server cares and takes pride in their work. Imagine if someone was trying to conduct business and can't even place a pad of paper on the table.
This brings forth another important point. Servers need to work as a team to ensure that each others section is free from clutter. Now I am not saying to consistently intrude on your fellow co-workers domain, but have an eye and offer assistance whenever possible. It all works out in the end and the person that benefits the most is the guest.