This right can be more valuable to the developer than the actual fee received from the client. Both the developer and client prior to beginning work should understand the level of this effort. The client will probably want the developer to regularly back up the site, so that if the developer's server crashes, the site can quickly be installed on another server. Furthermore, the client will want possession of a current backup copy so that if the client decides to move to a different server, the client does not have to wait for the developer to deliver a disk. When a company depends on its website for a large portion of its business, then it can incur large losses when things do not go right.
Developers can contractually shield themselves from liability for such losses.