Can anyone say at what scenario we should do iisreset and Apppool recycle.I have MOSS installed

IISreset resets all application pools.

Application pools are used to seperate processes. In earlier versions we always had to reset IIS, and so resetting ALL websites.
When resetting an Application pool, only the websites configured to use that application pool are reset.
All other websites (that are configured to use other application pools) keep on running.

IISreset is actually nowadays only to update server settings.
However, it's used very often instead of een application pool reset.

Thanks Eric
But I heard from my Colleague that for example in Sharpoint Perspective if a user is Uploading a Doc to a Site
if we do Apppool recyle it will not affect his Document Upload but if we do iisreset he will loose his session

Is that correct

You can't say it that hard.
It's possible the session is lost and it's possible the session is not affected.

Look at this site for more information : http://msdn.microsoft.com/en-us/library/ms525803.aspx


Kind regards,

Eric van Glabbeek

Correct, IIS reset kill all current session, while recycle it will start a fresh new IIS worker process, old session are still intact, the purpose is to free memory usage