Rescan. In need of an explaination please.

[Cynyster]

Hello all. Been a while since I posted.
The program has been working perfect for me.

My question is about the rescan feature.
What is its purpose and what is a viable setting for it?

I have it set to the default and I see it rescanning my headers and the only thing I notice is I get a lot of duplicate auto downloaded attachments.

(such as my auto download of the alt.binaries.pictures.wallpapers)

Thanks for any help here

Cynyster