Located on the Miscellaneous category tab in Search Builder this Condition will give you just the Primary Adults for those in your search. The best way to use this to ensure that you get the result you intend would be to run your search and then add this Condition to end up with the parents. Using this Parents Only Condition will apply to the entire search, regardless of where in the search you add it. In other words, you cannot apply it to only a single group inside the search.
If you want the parents of one group and the members of another, run the search for the parents first and tag everyone. Then build another search the contains your tag and the other group.
You want to find all the regular attenders who are members of Children’s Life Groups and then you want to find the parents of those children. Use the Enrollment Condition “Is Member Of” and select the specific Program/Division, then add an Attendance Condition such as “Attendance %” and specify the same Program/Division. Run the search to find the children. Once you know that you have the group of children you want, then add the Condition “Parents Of” and Run. Now the results will be the Primary Adults instead of the children.