The only times we have every requested partial payment in advance have been on large, complex commercial jobs.  On most of the jobs of this nature, ones that take several months to complete and cost in excess of a couple of thousand, we expect payments as work progresses.  I've never taken a request of this nature from a new client though, in that case I suppose I would expect larger payments earlier in the project.
For a regular residential job, I agree with Robert.  I want to get the job out quickly to assist the client.