Ciara said:
May not be relevant but my OS is in C:\ on my 1st Hard Drive and all programs are in Programs2 D:\ on my 2nd Hard Drive ... so the size of my OS stays the same if applications are added or removed

I personally wouldn't like installed applications to straddle partitions never mind disks. There isn't a clean separation between the OS and these programs. One example is the use of the registry. This doesn't apply to standalone programs which aren't installed, but in my case they are in the minority. I want one imaged partition to provide me with a fully functioning system when reimaged.

There is a much cleaner boundary between data and the OS. Much of it may not change much but could consume more than your OS and programs combined. So you would probably adopt a different backup strategy.