There is a lot of debate over the value of certification and I'd like to add my 2 cents.
Like many in this field, I became a defacto-dba via support for end-user applications with SQL (and FoxPro) back ends. I found that with a good set of instructions and minimal knowledge, one can install SQL Server, a third party application that connects to a database, and the whole system might run for years in manner that does allow users to get their jobs done. The problem is that performance issues might occur, or the system may crash for one reason or another, and the defacto DBA need to be able to do something other than reboot the server.
And even then, once you get a good backup routine in place and you're learned the difference between inner & outer joins, your site probably STILL doesn't utilize all the features of SQL Server. If many SQL Server features are a mystery, your users may not be getting all the benefit they can get, may be suffering unnecessary performance issues, and may be at risk for security breeches. And if you find yourself job hunting, the company you want to work for may be looking for knowledge & experience in functions you know little about.
In my case, I've found that studying for certification has exposed me to many more features of SQL, some of which I've started using to my employer's benefit without them asking me to do it (unless your bosses are DBAs, they wouldn't know to ask you to do them). And as for other features I've experimented with on my VM at home but have no need for in my work environment, these may be among the skills being sought at my next job interview.