Putting SQL Server data files in a different partition
It won't matter for performance but it could matter for other reasons.

To get better performance, you need to have it split across different physical hardware; splitting files across logical partitions does not help or hurt performance. But I wouldn't worry about this unless you start seeing disk activity as a bottleneck.

There are benefits from this approach:


You can back up the D: drive without having to do a system image backup.
You can restore the D: drive without restoring the entire system. 
If you get to a point where you need more space, it is easier to move the D: drive to another physical disk than to have to move the C: drive or relocate the database files.