You shouldn't need to do that either ;) I suppose it depends on your definition of "constantly" but you can overdo defragging and just put extra stress on your poor old HDD. There is a lot of online arguments over how often is "too often" and what %age of fragmentation should cause you to defrag. But I've frogotten for months on end and hardly noticed any difference - and I am like you I have a lot of stuff installed all the time and am constantly putting stuff on and taking stuff off.

And if you get an SSD don't bother defragging it - its ponitless. An occasional "compress free space" is all you need for an SSD and some even argue against that.

If the OP is using Win7 then by default defragmentation is scheduled to run at regular intervals, so there's absolutely no need to run it manually.

dont forget it is also more dependent on the number of times data is written so if your uninstalling and reinstalling stuff like crazy or downloading data for example on a constant basis your need to defragment will increase. Obviously only compared to those that do nothing at all what so ever but still its a consideration in the "to defragment or not defragment" question.

You are correct, but I don't think he is:

If im right that would put it squarely in Vista territory.

If we are talking about a typical mechanical harddrive I always try to leave 15% left so you can swap files and you leave enough space so you can defrag the files (which I believe is the main cause for most harddrive performance loss excluding hardware failure). On newer OS like Windows 7 and 8 defragmentation is set to auto when you're not using your computer so I don't think you will need to bother with that as long as you leave some space so files can be moved.

Currently you have about 16.5% free space, I would stop installing new games or applications that take any significant space for now until you can uninstall something else.