Mark Cuban hates meetings. Hates meetings. 

"...For the past 20 years," Cuban says, "I don't do meetings or phone calls. I'll do a meeting if you're going to write me a check. I'll do a meeting if there's a really good reason to help close a deal. Other than that, it's email."

Why? Meetings typically take a few minutes to stagger to a start. They usually drift to a close. To Cuban, all that chatter -- while certainly pleasant -- is unproductive. And that makes him less effective.

Science agrees, albeit for a different reason. According to a 2012 study published in Transcripts of the Royal Society of London, participants who were placed in small groups and asked to solve problems experienced an individual IQ drop of approximately 15 percent. 

Yep: Attend a meeting, instantly get dumber.

Disinterest and boredom aren't the only causes. Social cues also play a role. According to the study, if you feel your contributions won't be appreciated, much less valued, your IQ drops. The same is true if you feel like you have less status, whether formal or informal, within the group. 

And then there's this: If other people criticize your contributions -- anywhere on the spectrum from full-on Steve Jobs to mumbled disagreement -- your IQ drops.

As the researchers write, "Results suggest that individuals express diminished cognitive capacity in small groups, an effect that is exacerbated by perceived lower status within the group and correlated with specific neurobehavioral responses."

All of which is a fancy way of saying that you need to hold fewer meetings. Any meeting that won't directly generate revenue or cost savings -- either in the form of a key decision or a concrete plan of action -- is a complete waste of time. The only meetings you should hold are meetings that actually require a group to make a decision.

Which, if you think about it, are rare.

As for creating "buy-in"? Meetings don't create buy-in. Great ideas create buy-in. Great projects create buy-in. Tell me what we're doing, help me understand why it's important that we do it, and I'll buy in.

Then make sure you only invite the right people. (If Jeff Bezos could run Amazon with "two-pizza teams," you can run your business the same way.) 

Then, make the people you invite feel like an equal member of the team. (If you can't, don't invite them.) 

Then value their contributions. 

Only then will your employees be as smart during the meeting as they were before the meeting.