What are the implications of a deferential standard of review for a factual or mixed fact and law decision?

There are many sound policy reasons why appellate courts apply a deferential standard of review to factual or mixed fact and law trial decisions (see Housen v. Nikolaisen, 2002 SCC 33, at paras. 10-20; reaffirmed in H.L. v. Canada (Attorney General), 2005 SCC 25).

This approach applies to facts based on credibility findings, writ large, and to factual findings where there is no issue of credibility (see: Geffen v. Goodman Estate, 1991 CanLII 69 (SCC), [1991] 2 S.C.R. 353). In other words, deference is not tethered solely to the trial judge’s advantage of seeing and hearing the witness’s testimony. As to the trial judge being disadvantaged from not having observed the appellant’s demeanor, I say three things.