As you might already know Windows 7 default installation creates a 100MB partition during Setup.
The function is not really documented on the Internet, however reading this you should already know what it is for.
The partition in question is the System Reserved Partition.
So lets compare the Windows 7 installation with and without the 100MB System Reserve Partition.
Firstly lets take a look at the root drive of the Windows 7 with the 100MB:
Next lets take a look at the root drive of the Windows 7 without the 100MB:
So what is the the difference? It is the presence of file and folder required for booting like bootmgr etc...
Open up the 100MB partition and what do you know we are right!
So what does this means?
It means in actual fact the extra partition is optional has 0 effects on system operation.
So lets take a logical approach and think of possible reasons for this change.
1)Prevent Noobs from accidentally killing their Windows Installation by moving the boot files off C:\ to a partition they can't touch? Possible Very Likely
2)Optimize boot performance by moving boot files to the first partition(front part of the drive)? Possible as well.
3)Modularize the OS file layout? Very possible a much more elegant solution than cramping all the files into C:\.In fact it could mean you could multiboot multiple Windows OS on volumes without having repeated Boot files in each and every installation.
What does this means to end user? It means for those Dual Booters like me it is 4 - 2 primary partition left instead of 4 - 1.
Does it matter? No because you can create logical/extended partition to bypass the 4 primary partition limit in legacy Master Boot Record (MBR).
It doesn't affect GUID Partition Tables (GPT) on EFI systems.
Unfortunately Windows 7 doesn't do GPT volume installation.
So remember the 100MB is just a rearrangement of boot files. Period.