That's a good point. This question comes up so frequently on the boards it's clear that a lot of people aren't aware of it. And no wonder, since Garmin doesn't see fit to even mention it in the manual! I thought they did, but can't find any mention of it now.
just last night i was in the city with nearly-full batteries and took it off power saver and it went right down to an accuracy of 13 or 14. mostly 14 (which makes sense seeing it's the minimum). so i guess battery saver is pretty much "suckage mode" lol
on a side-note, i installed city navigator on it (because i can lol) so now i got 2 driving gpss lol