So there are a few things here that are qualifiers.
1. I give them a space that they can use for when they want to be left alone or need to collaborate with one person. And I give them the technology to be able to do that. (Surfaces, docking stations, network shared files, etc) they can still choose to work in an enclosed space.
2. We are a relatively young company, and the observations made in the open area help speed up the development of SOPs and help to stop new people from stepping in the same hole so to speak.
3. The work can be done from anywhere and they sometimes do work from home as well. They are encouraged to use company cell phones to build a stronger relationship with the client, so the desk phone is almost superfluous. The desk itself is merely a home base.
There is a certain amount of unproductive time, however, remember this is the sales dept, they should be out at the clients site or running down opportunities. If they are at the office they are preparing quotes or working through a design (we don't have sales engineers, our sales guys need to be competent in design and problem solving). When they are working through a design I often hear them asking for collaboration in problem solving or for someone to verify their solution.
There are drawbacks, but for me, at this time, while building the operations and improving the way the business itself works, the good outweighs the bad.