I ranked first at a t25 and transferred to U.Chicago.
Correlation doesn't imply causation, though, so I cannot say if it was worth my time.
FWIW I briefed every case my 1L year and am still doing it this year. Finished top 1% at a T2 and transferred to Berkeley. It takes more time up front during the semester, but it makes putting together an outline at the end much easier because you don't have to flip back through your book; you can just copy paste sections from your notes.
I subscribe to the school of thought that it's better to be moderately busy the whole semester rather than not busy until reading period.