What is the purpose of the "Switch tracker" button in the trackers list and why is it disabled sometimes?

It seems that this button is only needed for private (your own) torrents. And only if more than one tracker is specified when creating them.

Hmm. OK, adding trackers to the initial list indeed enables the button, but removing them doesn't disable it. And what does "switching" the tracker means? Enabling it? Disabling all others? And how can I tell in which state it is?