If set to true, then all Nautilus windows will be browser windows. This is how Nautilus used to behave before version 2.6, and some people prefer this behavior.
If set to true, then Nautilus will have a feature allowing you to delete a file immediately and in-place, instead of moving it to the trash. This feature can be dangerous, so use caution.
Speed tradeoff for when to show a preview of text file contents in the file's icon. If set to "always" then always show previews, even if the folder is on a remote server. If set to "local-only" then only show previews for local file systems. If set to "never" then never bother to read preview data.
Speed tradeoff for when to show the number of items in a folder. If set to "always" then always show item counts, even if the folder is on a remote server. If set to "local-only" then only show counts for local file systems. If set to "never" then never bother to compute item counts.