I had a client ask about this dialog box the other day. They thought that it was a bit confusing and wondered if it would affect the site model. The answer is that it only affects the visual presentation of the site model and does not affect the mathmatics behind the model. The Maximum and mimimum settings are used to filter the presentation of the model to the elevations that you want. The reason for the dialog is that something that you have created (something that affects the site model) is above the maximun elevation or is below the minimum elevation. Vecotrworks is asking if you want to change the maximum and minimum settings so that you can see the new obejct and its affect on the site model.