You have been in both kinds,, and you don’t need anyone to tell you the difference. The meeting that drains announces itself right from the invite

Your brain is not a machine. It does not run at a constant speed from 9 am to 5 pm; in infact, till 9 pm for founders and operators. It does not maintain the same quality of thought across an eight-hour workday. It does not have an off switch that you flip when a meeting invite arrives.

This meeting neither has an agenda nor a decision to make. It usually has about nine attendees, and three of the nine haven't spoken since the second week this meeting was scheduled.

Your calendar has no say about what happens inside a meeting. It does not know if a decision meeting produced a decision or a follow-up meeting. It does not know if the eight people who attended were the right people, or just people who accepted an invite because declining felt rude. It does not know whether the discussion required everyone in the room or just three people, with the rest present out of courtesy. All the calendar knows is that a slot existed and someone filled

The calendar does not ask whether a meeting should exist. It only asks when, and because nobody built a system to answer the first question, the second question gets answered 12 times a day, 5 days a week, until everyone is booked, busy, and still somehow behind the production schedule.