With summer in full swing, you're probably trying to get the most you can out of your AC. If you want to maximise your AC's performance, don't close too many air vents and ruin your home's airflow.
As tips site How-To Geek points out, houses don't always cool down evenly. If one area of your home gets cooler than the others, you might be tempted to close a few air vents. One, maybe two is fine, but closing too many can overwork your AC. Not only will it make it less effective at cooling, but it can cost you more money:
Closing off vents uses more energy, because your system is working harder in order to push past the increased pressure that closed vents create, especially if you have a variable-speed system fan that can change speeds automatically. If you have an older system, then it's likely that the fan remains at a constant speed, which is still bad news if you close too many vents, as the increased pressure will simply slow down the fan's speed, resulting in less airflow.
A ton of other factors can also cause problems when you close vents. Ductwork often isn't sealed, which means adding pressure to the system can force air out of the ducts themselves. If you have smart vents, they can also cause problems, since they're not really that smart. Essentially, if a room is too cool, try adjusting your thermostat overall to find a nice balance for the whole house, or consider a sweater before you close too many vents and rack up a huge bill for no benefit.