Manfred could answer better, but I think this trick is designed to help with point of view.

The problem with anthropic problems is that you aren't sure which you is you. There's all sorts of branches that occur, and you don't know which branch you're on. You're trying your damnedest to look backwards up the branching probability tree and hoping you don't lose track of any branches.

By pretending you're the researcher, you're looking at possible branching futures the other way. You always have a frame of reference that doesn't change subjectively, and doesn't need updates. At least, that's how I think it's supposed to work.