Given how ridiculously cheap HDDs are these days, why would you need to partition anything? If you want to shove your data to a different drive, get a different HDD. Same organization, double the capacity and greater performance.
Also, as already said, if you run out of space for your OS partition you have to mess about repartitioning. As safe as it is, it is still an extra pointless process that could go wrong.
Almost all Windows software assumes C:\ for all the default locations so you will have to take extra steps every time you install something to make sure it goes somewhere else. Plus there is a really good chance most of your software will need to be reinstalled upon a Windows reinstallation/upgrade anyway, so why bother installing it elsewhere?
