If it made no difference who testifies, then prosecutors wouldn’t care who testifies.
But prosecutors put very intense efforts into these arrangements.
In this case, the prosecutors were caught off guard. They failed, and they failed big.
The prosecutors certainly cared who testified when they dropped Karen McDougal from the witness list after Stephanie Clifford's disaster of a testimony.
And they must have had doubts about Cohen's testimony if they brought in rookie New York Democrat Congressman Dan Goldman (who represents Brooklyn and lower Manhattan) to coach Cohen's testimony.
-PJ