Hmmm, if you've never watched (or paid attention to the details as) someone worked through all the stages necessary to complete a job you're at a bit of a disadvantage. ;^)

The answer to your question really depends on what you do, your business model (how you do it) and the relationship style you want with your clients.

I don't see why you need to do much more than state parameters in your contract and then use email or comparable to inform each other of your progress. If you're dealing in contracts worth hundreds of thousands, or you're dealing with particularly sensitive issues, then a formal (i.e., a notarized statement) interim acknowledgement of completion might be called for. Otherwise, I don't think so.

But I say this with no special information about you, your business or your clients.