If you're using a hard drive rather than a SSD, defragmentation will still reduce disk performance. Because of this, starting with Vista, the standard Windows defrag autmaitcally does a defrag in the background once a week. While Microsoft's defrag software actually works very well, in some cases you will get better disk performance by using third party defrag tools. But, it's worth noting, that in some cases you will actually get better disk performance from using Microsoft's defrag software, rather than third party software. Because of this, for most people, the best option would be just to let Windows defrag your drives weekly, rather than installing other defrag software.Isn't degrag history? Why still do it?
When it comes to SSDs, due to the way they work there is little need to defrag them. Despite what many people claim, it is actually safe to do so, but there's just little point in doing so. Having said that Windows itself does defrag SSDs, It dosn't cause any harm and generally shouldn't be disabled.