Downloading apps outside of the Mac App Store is safe, but, as with anything online, you need to be careful about where you find software for your computer. The Mac has been available for over 40 years, but its App Store only arrived in 2011, followed by the striking success of the iPhone App Store, which means that for the longest time, Mac users didn't have an "official" place to download the software they needed. Seeing how popular the iPhone App Store was becoming, the company decided it would be convenient for users to have a single place where they could find, buy and download apps using the iTunes (now Apple) Account. Over the years, Apple added to the discourse that the App Store would give users peace of mind, as every app would undergo rigorous testing, avoiding malicious apps, software that could steal your data, or explore possible security flaws. Still, while many Mac users do take advantage of the Mac App Store, there's no real reason why someone should only download apps from there, especially because computers, in general, always worked differently than an iPhone, for example.