All this is on-line storage, for which PC World ants you to pay for. That means that if you exceed the memory capacity of your device, than you will be able to save things to this Cloud, ie on to the 'net.
But consider how you are going to retrieve this stuff that you have saved.
You will have to go on-line to get at this data that you have saved. What if you are in a place where you can't get wifi ?
If you think that you will saving lots and lots of stuff, like photos or movies, consider using a simple portable hard drive. I use one made by Toshiba, similar to this one :::
http://www.ebay.co.uk/itm/Toshiba-1TB-StorE-Basics-USB-3-0-2-5-Portable-External-Hard-Drive-Matte-Black-/360847454928?pt=UK_Computing_HardDrives_RL&hash=item54042f32d0
There plenty of others, some much cheaper. Its the size of a cigarette packet, weighs b*gger all and simply plugs into your USB socket. It took about 2 mins to set up and you can use it anywhere. It doesn't need a wifi signal and you can move it around as many different laptops, etc as you like.
Cloud is simply a way for PC World to make more money out of you, for something you don't need !