Many suppliers now have online tariffs enabling customers to view their bills online and also submit meter readings via email or the web. This means that the energy supplier does not have to send out so much paperwork to you and also because you submit your meter readings, they often offer a discount.
Online energy bills will be more accurate as your charges are based on your actual meter readings, rather than readings estimated by your energy supplier. This minimises the chance you will overpaying for your gas and electricity, or getting a nasty surprise when your energy supplier informs you that you have used more than you have paid for.
With online energy tariffs, suppliers usually have a website which enables you to view your bills at any time. No need to keep paper files which can get lost or damaged.