Yes it is a living document and i agree with everyone here. However, you can’t look at this like a file on your laptop. These changes and processes actually cost money and time. When you are hired for a project, you are expected to meet the client’s requirements. Client’s don’t change their minds on a regular basis, because every change they want to do essentially is costing them money and revision of all the paperwork. This can be challenging if you have worked on a device for a long time. The most common time for revisions would be if there is an actual demand on the market. That my thought on this is it depends on the business and satisfying the client. This industry is driven by money so some companies may advise for multiple revisions due to the fact that is more money and time. So it depends.