There is NEVER any negative to keeping a clean, lean and mean PC.
You can move files using Windows Explorer or with a simple batch file.
I don't like the move command, because if something goes wrong, you can loose valuable data for ever. Doing a copy and delete (after you've verified that the copy worked the way you want) is the safest way to perform a move.
The smaller you can keep your C drive, the less time it takes for your hard drive to find the next file you want to access. It doesn't have to jump over all the garbage to get to the good stuff.
Also, the fewer files you have on C the faster your searches, scans and defrag's will run.
People are all the time griping about a Spybot scan or a virus scan taking over an hour. If they would just clean all the crapola off of their drive, those scans would run a lot faster.
I have to deal with this stuff daily, in my PC business, so I am painfully aware of that which I speak.
One little trick I pull to keep a PC somewhat clean, is to install a batch file in the Startup Folder, that deletes the contents of all the temp folders on the HD. That varies from PC to PC, so one size does not fit all.
Then by running "Disk Cleanup" and doing a periodic Defrag, one can keep their HD's running at peak performance. I've been doing this for years and it really does work!
Cheers mates!
The Shadow