Overhead panel - auto land alt query?

Hello:For a while I've wondered what the switch in the overhead panel lower right marked Auto 35000 and Land Alt is? I cannot seem to find mention of it in the manual in such a way as to explain its reason for existence and how to use itI realise Land Alt is landing altitude - but what is it used for?Is it simulated in FS9?When would I use it?Thanks......IAIN