3.1. Relevance of the evidence
In T 361/00 the board explained in detail why, given the circumstances of the case before it, hearing the witness would be unnecessary because it would in no way affect the outcome of its decision. (In the same vein, see T 377/17 regarding witnesses offered for carrying out the furnished tests.)
As per T 41/19, an affidavit was one possible form of evidence and could therefore be taken into account as stand-alone evidence. This being the case, a written statement carried no less weight than hearing the author of the statement as a witness.
In T 1410/14 (prior use – train – test drive) the board remarked in particular that, since the witness whose hearing the opponent had requested would not have been able to testify as to the decisive material facts, such a hearing would serve no purpose.