A trial lawyer finishes a case knowing things that are not in the record: what the witness was like, what the jury responded to, which ruling felt wrong in the room.
That knowledge is invaluable at trial and actively dangerous on appeal.
The cold record problem
The panel has the transcript. It does not have the room. Arguments that depend on atmosphere — the witness was obviously evasive, the court was plainly frustrated — do not survive the transition to paper.
Worse, they read as substitutes for record citations. A brief that gestures at what everyone present understood signals that the record does not say it.
Why fresh eyes help
We read the record the way the panel will: cold, once through, without knowing what was supposed to be important. Where we get lost, the panel will get lost. Where we form the wrong impression, so will they.
That first-read reaction is difficult for trial counsel to reproduce, and it is the most useful diagnostic available.
Working together
This is not an argument for excluding the trial team. They know where the bodies are, and no amount of record review substitutes for that.
It is an argument for separating the two jobs. One person knows what happened. Another person knows what the paper says happened. The appeal is about the second.