I don't use the exact tools you speak of, but those are really important. I'm assuming disk cleanup removes temp files. You should regularly remove cookies and delete temp files from your computer. I have my browser set to delete cookies upon shutdown. I also don't save my browsing history and I definitely don't have my browser save any passwords (security reasons.) Doing this saves me space and makes it so that I don't have to delete a bunch of data at once.
If you've never done a file clean-up, you'd be surprised how much hard drive space is taken up by just junk. Think of it this way: With every single website you visit, every single image (even little teeny, tiny icons) is downloaded to your computer and stored in temp files. Think about the space all that takes up!
Defragging rearranges memory which is extremely helpful in speeding up your computer, especially if you have software suites and games installed. Think of your computer as if it's a closet where you keep a bunch of board games (and you have rude kids.) Each time they open the closet, they mess it up. (This is when you download & install software, uninstall something... delete things, add things, etc.) Next thing you know there are dice all over, you've got uno cards all over the closet, and your monopoly game is essentially taken apart bit by bit and strewn all over. You want to play monopoly, but it takes forever to find ALL the pieces so you can play. Defragging is taking your closet and cleaning it, putting everything in its rightful place so that next time you want to play Monopoly, you're able to just grab it and go.
Hope this helps!