Data Connection/Radio on or off?

[Nagual]

I just read yet another post stating that having the Data Connection on in Comm Manager full time is a battery drain.

Now I'm looking at it and oddly enough it seems to have turned off on its own (or more likely, some app or setting turned it off) but I usually have had it on full time.

I have read many posts and threads on this forum and still can't seem to get a clear answer. Is it possible to get a more or less definitive one?:

Does it or does it not make a difference in terms of battery life and functionality whether this thing in Comm Manager is on or off?

If it's set to off, will it save battery life? And then when a program requiring data, like the web browser we often use, will it be re-enabled only during that time and then turned back off when no longer in use?

If it impacts the functionality of the phone (preventing data-requiring apps from working when launched) and saves virtually no power, I'd rather just switch it to on all the time. (Never mind why it sometimes seems to turn off on its own.)

Please share your knowledge, because this is one of the most confusing things about this phone to me.