Effect Immediately is required to top up the plan immediately after recharge.
For example: If plan A has expiry date as 10/06/2009. The plan is topped up with a validity of 10 days on 09/06/2009. If check box effect immediately is selected while defining the plan in Price Plan screen, the plan is topped up immediately that is on 09/06/2009 and the expiry date will be 19/06/2009. If the check box is not selected while defining the plan, then the plan is topped up the day after the expiry date that is on 11/06/2009 and the expiry date will be 21/06/2009.