One requirement for the home office deduction is that you regularly use a part of your home exclusively for conducting business.
Example: Let's say you turned an unused bedroom into your office and installed a computer with its own high-speed connection. You go in there 4–6 days every week for your self-employed job building websites. The room is used strictly for business—contacting prospects and clients, meeting with them, and working on their websites. In this case, your office would meet the regular and exclusive use requirement.
On the other hand, if you or a family member occasionally go into your office so they can watch movies or play games on your computer, your office is no longer being exclusively used for business.
Similarly, if you work out of your office occasionally or sporadically, it wouldn't be used regularly.