Read this recent thread by me while I was talking to Umberto about it for more detailed info.
http://www.fsdreamteam.com/forum/index.php?topic=2434.0In a nutshell, it controls when the pop up scenery loads into view. The higher you set it the farther away from the airport they will load. For KFLL I had to set mine to 4 to help eliminate the slight pauses while the items loaded into view. I believe the highest setting is 10, which would load all the scenery items while you are farther out. So if you leave it at default and are 1 mile away some items wont load into view until you get closer to them. If you set it to 10 and are 1 mile away, most likely all the scenery items will already be loaded into view, whether you can see them or not, but will cost more computing power. If you have a powerful rig, higher settings probably wont hurt your performance to much.
