New Data Source -> Existing Get And Transform Query
I find it common to create a singular Get and Transform query that performs a baseline set of commands that are then split off into various outputs. This creates a cascade of queries which is not particularly challenging via the Advanced Editor.
Source = Query_Name
As easy as that is, simply needing to access the Advanced Editor immediately many users away from the concept.
Something simple like having the option under "New Query" to select an "Existing Query" would be immensely useful and, I would think, incredibly easy.
The attached file demonstrates this in action. Making it possible for a client to more easily create a query that references another query as the starting point would help dramatically.