This customary way of getting signatures on documents is tedious and inefficient. And because of all the hassle involved, some people tend to procrastinate on signing the document until the very last minute, which adds further delays to the process. Getting documents signed in this manner also doesn't scale well.
It might be fine if you only need one or two documents signed in a year. But to facilitate and manage this process for hundreds of documents and for hundreds of signers is a nightmare. (Some examples of organizations that operate on this scale are web design agencies, law firms, and medical services.) And what if you need the document signed by multiple people?