How many similar controls warrant a mass action?

Let's say we have a modal with a number of similar actions. We're trying to decide whether a mass action to mark/clear all checkboxes is justified. The modal performs an infrequent action in the system, used maybe a few times a day by a professional user who works with the system for a couple hours a day.

The users would naturally like to have this mass action, because it "saves time" and because they're unaware of the downsides, like visual clutter, increased cognitive load and the general pettiness of trying to save every possible click.

And at a certain number of controls it does appear to be worth it. How can we determine where to draw this line?