In order to back them up, Time Machine has to copy the disk image file. If you make any change to the contents of a disk image, the entire file winds up copied to Time Machine.

Win32 Disk Imager is a free tool for Windows to write an IMG file to removable device and backup your removable device to a raw image file.

It can be tricky to manage disk partitions in Windows. Perhaps you want to boot two operating systems simultaneously, or maybe you don't want to reinstall Windows when partitioning a hard disk.