What for Archive & Install?

[MBX]

What's the archive & install option good for if you can't really re-use it according to this apple site: http://docs.info.apple.com/article.html?artnum=107120

"You cannot start up your computer using a Previous System folder, nor can you "re-bless" the Previous System folder."

 

[JNB]

The utility is that absolutely everything from the prior install is still extant on your machine. That way, if there's anything in the old System directories squirreled away that might need to be copied over for some reason, it's still there.

It was never intended to be re-used. If you need to maintain the Tiger boot, then you should do a clean install of Leopard on a separate partition/drive.