The time you gain from an automation fills up again immediately because it comes back as crumbs, not as a block, and a gap nobody has assigned goes to whatever is loudest. You keep the gain by assigning that time, before the automation starts, to one task with a fixed slot and a result due after four weeks.
Read the full article: https://impruvement.com/blog/why-the-time-you-gain-from-an-automation-fills-up-again