Why Must Acronis Delete My Data to Make a Backup?

Acronis Home 10
Win XP
2 hard drives

Why does Acronis have to cause the loss of data to clone a backup image?

When attempting to clone my C drive, I got the following message:

"The destination hard drive you have chosen contains some partitions that could contain useful data. Click OK to confirm deletion of all the partitions on the destination hard disk drive."

I am given the impression that if I allow Acronis to delete these partitions, there will be a loss of the data that is in those partitions.