What is the 100Mb Partition FOR?

Bitlocker and possibly startup and recovery tools. If you don't use bitlocker then you do not need it.

 

And bitlocker ist only supported by Windows 7 Ultimate and Enterprise.

 

It holds the boot files, to prevent them from being overwritten or damaged when repartitioning.

 

I don't understand your argument: When the main partition dies whilst a re-partition action – what for is it good to have the 100 Mb partition ?

 

I often have several Windows partitions and I reinstall relatively often, and it is very handy to have a separate boot partition. I have done it for several years and the reason for it is simple:
Removing a windows installation and leave the boot files is a tiresome process. It is far more easier to just format the partition you want to install to, knowing that the boot files are on a separate partition. A tiny bit of editing with BCDEdit is also needed.

I almost never install Windows from a boot media on a physical PC, always installing it from another Windows partition. I made the switch from 32-bit to 64-bit several years ago, that was the last time Insstalled from boot.

 

Too right, we should be able to partition ourselves and it should be upto us, how we do our computers.

I just use my bios to select to boot from which hard drive.