Let’s say you set up a custom filter that has 3 rules: find all direct ancestors to 4 generations, find all descendants, find everyone within 2 degrees of separation of that same focal person.
And it works just the way you hoped.
But then you want to look at the same relatives originating from a different person and 5 generations of those ancestors.
You could use the standard editor and drill down through all those rules and carefully tweak each one. (Which means remembering which category, switching to that view category, enabling the Gramplet sidebar, switching to the filter view, navigating to the filter Gramplet, switching to the right custom filter, hitting Edit, double-click on each of the 3 rules in turn, navigate a selection dialog for each of those rules, remember to change the ancestors generator count. And then worry that you missed a setting. and then FINALLY you can run the filter.
But… if you use the FilterParams tool, you can do all that from a single form. And change the focal person in all 3 rules by changing 1 ID field.
It is FAR less complex.