wi-fi ask to join network on or off - what's the difference?

its not quite as described above but close, it goes like this:

When it is set to ON, and if there are no known networks (networks you joined before), the iPod will ask you if you want to join any available network if there is one within your range.

When set to OFF, the iPod will still automatically join the network you are used to, but if your network is not available, it will not pop up a message asking if you want to join some other network that is within your range.

Is it confusing? lol, the thing is, I leave it OFF, because it doesn't pop up some message asking if I want to join this or that network if I'm away from my default router all the time.

If you joined the network before then YES, it will join it automatically, if no previously joined networks are available it will not join, well, thats what I experienced with my touch 🙂

With it on, the iPod will automatically connect to any network you have already previously connected to.

With it off, the iPod will never automatically connect to a network, you must always do it manually.

It's good on, because then you don't have to manually do it every time (especially if the network requires a WEP/WPA key).
It's bad on, because if you're network is defaulted (like named "linksys"), you're iPod would try to connect to it if it was named "linksys".

Well if your connected on but if your trying to save battery power off. It searchs for WiFi networks