I had attempted to use something like this to bring in data from an external file. One of those "ugly delimited" files, kind of delimited and kind of not, that I needed to bring in. This would have offered a way to parse it and clean it up in one single shot, and I would simply need to insert the results from the TVF into my destination table, skipping the whole staging table, clean up the data, etc...

I ended up abandoning it because it was trying to build the entire table in mem before returning it, so the CLR function would crash before getting anything out. So - I ended up going in another direction and got it done that way.

I had also looked at building the old running totals this way, running into the same problem (order is in fact guaranteed this way so no controversy over documented vs not). I got around that using the CLR SP (since you can stream the results without having to build the entire return set first), but still use the "other way" until I am formally forbidden from doing so , since it is still faster than the CLR SP (although not by a whole lot).