I'll take the bait if no one else will.
A calendar is useful for one thing: pinning events that will happen at a known time and being reminded of when they are about to start.
If you need to keep extensive notes on projects, understand how late or accelerated tasks will impact other dates, break down work into steps, track progress on a project or individual task, create lists, map ideas, inventory items, archive knowledge, or sketch workflows, a calendar is worthless.
This story is not true.