Earlier quoted context omitted.
That courtesy is almost always bad practice and is generally unlawful. You must yield right of way to a pedestrian at a legal crossing, but california has codes that prohibit impeding normal traffic flow, including stopping in the street to wave across a pedestrian where there is no such crossing. It's especially dangerous on multi-lane roads because the stopped vehicle can blind the pedestrian to other traffic.
I think the comment you're responding to was referring to needing to cross a backed up lane of traffic in their car, not on foot.
Sure, there are valid scenarios. LA certainly has some terrible and legal vehicle crossings. (The fast, windy portion of beverly ranks.) I agree that it's hard to navigate without some cooperation. It's just that almost all of the crashes I've witnessed involved someone giving a bad go-ahead.