People who document the "how", or worse, the "what", generally do so because they're bad at reading code. I work with a few people that do this and they readily admit that that is the reason why they feel the need for comments of the form...

     // set the user data
     var userData = {

The thing that grates with me is that this is apparently an acceptable stance on the issue. These people don't see this inability to read plain code as a flaw, or something they should work on.