how often should a computer be defragmented?
How often to defrag would depend on how fragmented your drive gets and how fast. The analyze feature in a defrag program should give an idea. Some people delete/edit and add files so frequently that they defrag daily or once every few days. Others defrag once a month or couple of months. It would depend on each user.
Hello, I've been defragmenting my computer weekly along with the disk clean up. Is it dangerous to do this? If so why would it be?
Not really since even if you do run a defrag on a drive that has hardly any fragmentation, it doesnt have much work to do anyways and completes in a few minutes.
In fact defraggers like Diskeeper run in real time on automatic mode and defrag whenever required without affecting other programs and system resources. They keep the drives defragged very safely.