Ask about Clear Data Before Push in Data Maps

Hello everyone,

I have one question about the Data Maps to push data from the BSO cube to the ASO cube.

When I tried to run the Data Maps, it showed the popup asking, "Do you want to clear the data before pushing?":

My setup now for the data map is:

I just defined the source (e.g., Ilvl0Descendants(Intercompany), Ilvl0Descendants(YearTotal)) and didn't define the target.

My question is:

When I click "Yes," what will happen in the ASO cube? Is it will clear only the dataset that I set up for the source, or will it clear all data in the ASO cube if I don't define the target - only keep the target as Intercompany, Period, and Plan Element like the picture above?