I guess it runs on the parent members if none of the members are selected.
Apologies if my guess is wrong and happy to take outputs on this.
With an ad-hoc Planning connection in Smart View, you will be prompted for your variables. It will run for whatever Customer and Product you specify. (FYI - I'm looking at 220.127.116.11. I suppose earlier versions could be different.)
Hope this helps,
it will use the default values given in the variables. When nothing is specified, or the member names have been changed/does not exist, it will crash and tell you what is missing.