You can install apps on every Mac authorized for your personal use and even download them again. This is especially convenient when you buy a new Mac and want to load it with apps you already own.
If you are a private consumer, licenses you purchased in the Mac App Store are valid for an unlimited number of computers that you own. So there is no need to buy more than one copy.
Company or organization
If you represent a company or other organization, a license bought via the App Store is valid for either one single computer or one single person using multiple computers. For details in this case, please click the link App License Agreement which is displayed on the page of each App in the App Store.
Does that mean I could buy one copy of an app and install it on every Mac in my business?
No, the licenses you agree to when you enter the Mac App Store says that app downloads are for Macs that you personally own, and that’s a license for personal use. Apps that are intended for business and professional use are licensed differently, typically to you or for a single computer, but used by several people. While there’s no technical impediment to you installing them on multiple Macs at work, you’ll be violating the license agreement. It’s the same scenario as if you buy a single-user copy of iWork and install it on ten Macs at work—you can do it, but you’re violating the license agreement, making the act ethically questionable.