Updating Profiles/Reconciliations

Hi there, I'm just a little unsure of when you would update (e.g. attributes on) profiles and when you would update the reconciliation for the month itself?  If you updated the reconciliation, obviously when the profiles are copied to the next period, then your changes would not be, so not sure when you would want to do this? Could you please explain when you would update profiles and reconciliations? Many thanks