Is disk cleanup necessary, if yes after how many days?

Answer 1

Disk Cleanup, Scandisk, defrag should be run at least every two weeks. The best part is the more frequently you run them, the less time they take.

Answer 2

Not necessary, but it removes stuff from your hard drive, so you are freeing up space. I don't ever use it thought. Depending on what you normally do with your computer, it can have little amount of space (less than 10 megabytes)to a lot (above two gigabytes).
But if you want to do it often, do it about once every three to six months.
Note: Unused files/folders for about 50+ days will be compressed and take up space, so it is worth doing if you have lots of programs you don't use often.

Answer 3

If your harddrive is tiny, say 4.5 gig yes, do it. But if you have a 60 gig or bigger, forget it.