Again, I believe my question about string concat was incorrectly closed as Duplicate.
Why? As stated in the comments:
In fairness, that is definitely not a duplicate question - it focuses on why StringBuilder is faster than separate string concatenations, not on this specific question on why the alternative syntax also works on StringBuilder and whether the two are functionally identical. Also, there's some stuff in that other topic that isn't entirely true. In a well-prepared case multiple concatenations will never outperform StringBuilder, if you select it's initial capacity correctly with the alternative constructor.
On the top of my question I can read:
And then go see the duplicate question and read:
I know the obvious performance advantage to using the StringBuilder is in C#
Well I don't know them and it's kind of the point of my question. Can someone take a few seconds to look at it?