Native resolutions, etc

[freckleface]

Hi, I have a few questions on using arcade monitors, visual qualities of CRTs, and native resolutions (whether using an arcade or PC (CRT) monitor).

The first two things are technical.  I heard that though the Betson, WG, and Billabs are multi-syncs, that it's at least advisable to power them down between resolution changes.  Is this true?

Next, if the convergence is off, what effect does this have and can it be fixed?  With the contrast and brightness set right, and the screen blank or when in a game like Asteriods where there is very little saturation, if one sees areas that aren't completely black, what does this mean?

Last thing is, from what I've read I'm guessing native resolution determines the original size of the picture and in-game behavior, right? If so, is using hardware stretch and stuff really a matter of preference, and is there some difference in the actual clarity of the graphics?

Thanks