[jakubp]

I've done backlogs before; both very high-level and very detailed; with and without mockups (even final graphic designs) and detailed description in the form of multi-page spec or user stories (depending on the fashion of the decade I was doing it in :).

I don't think having the detailed requirements made estimates much more accurate. However it made creating those estimates take an order of magnitude longer - developers needed much much more time to absorb all the details.

At that point I decided I only ever want to work with senior developers who have good imagination and can give reasonable triplets (solution, # of devs to do it, approximate time) for requested pair (idea, quality level).