This is a decent article, at least for the most part: I actually don’t like their examples for the “Preposition of Time” stuff at all, the versions with commas are just bad writing.

But basically it just comes down to whether the sentence/clause can be parsed unambiguously without the commas. There is no syntactical difference between “I as a German asked…” and “I, as a German, asked…”. It’s entirely a style choice.