What does 'Backing up your Ipod/Iphone' do?

So in a few weeks i'm getting a new iphone. Right now I have the Iphone 4, and Ipod 5. When ever I plug in my Ipod or Iphone into my MacBook at the top it always says Backing Up. I want to know what this is. And everything it does. Will it be a bad idea since me and my Mom share a computer? Also is there a way I can get all my apps, photos, notes, etc on to my new phone without re-downloading everything?

Its useful in case your ipod/iphone gets broken or if you lose it.

if your previous phone was an iphone you should be able to do so via icloud

Your apps, photos, notes, that's a what a backup is for. You sync the phone to PC every time you do this and iTunes will make an exact copy of the phone's settings, apps, photos, everything. Why? You might lose it, it gets broken, it gets stolen, or you buy a new one and want to import all of your stuff. When you set up your new phone you will 'Restore it from an iTunes backup'. This will import most things you want. You'll need an separate program to move your text messages from phone to Mac to phone but also use iCloud Control Panel installed on your Mac as well. Best luck.
http://www.cnet.com/...enshots/7/

http://www.gcflearnfree.org/macosxmountainlion/setting-up-icloud-with-your-windows-pc

1. Backup will make a backup file of your phone apps, photos, notes, contacts. In case you lose your phone data.
2. You can use a 3rd party software like this iOS file transfer to copy the apps, photos, notes, videos, songs and messages from your old iPhone to your macbook first, and then re-sync them to your new iPhone.