Of course, we did not have faculty as supervisors, but rather had much less-experienced GTA's. The individual carrels made the lab an unfriendly setting, and one could not even see a student on the other side of the room. The carrels are gone and we have scheduled labs now. By holding labs at night, we have solved the space problem for the time being. A concern I would have for open labs is that they would preclude group work, which often permits more replication.
Students have too much experience at running experiments with insufficient replication.
And employers are telling us they want students who know how to make group work succeed. Replication is important. Each student is expected to calculate the means and std. The advantage of this approach is that a fairly large data base can be obtained, and meaningful interpretation of the results can be made rather than attempting to make sense out of single observations. Students also learn about biological variability and designing experiments with adequate controls.