Quote: Originally Posted by LobsterEar
... if I save or download something OS related will it know which partition to use or will I have to choose? The same with non-OS stuff, will it instantly know which partition to go under?...
Things like Windows Update files will automatically know where to go. Other downloads can generally be directed to a folder of your choosing. (I send all my downloads to a folder which I cleverly named "Downloads".)
Some programs like to save things to other places (typically "My Documents") but they are going to do that whether you have separate partitions or not.
The biggest advantage I see is that you can separate files which aren't modified much, such as videos, music, etc, from your Windows partition which is going to contain files which tend to get shifted around somewhat.
You can get really creative with partitions and put your swap file on a partition of its own, typically a very small partition located at the fastest part of your hard drive which is at the beginning of the drive.
EDIT: I type too slow. Jonathan said it quite well and in a lot fewer words.