Hello Seige and welcome to English.SE!
I'm not an English teacher, but I personally consider that you can use "as to" in any sentence in which you could use "regarding".
Eg. 1: Would you be so kind as to elaborate on the subject?
Eg. 2: Could you please provide more information regarding the subject?
Both are polite to say, but "as to" has a different flavor.
Eg. 3: He was uncertain as to which road to take.
Eg. 4: He had doubts regarding the path he should take.
Though the phrases are different, they provide the same message. Also, "as to" gives you more choices of words and syntax.
Hope this helps!