As a quick review: Sandboxing refers to compartmentalizing what data and features a specific app is granted access to; apps each can metaphorically play exclusively in their own sandbox, accessing only that data which Apple has granted that app entitlements to see.

Originally, Apple told Mac App Store developers that their apps would need to implement sandboxing by November 2011. In November, that deadline was extended to March 2012; in February, . And as iCal will tell you, that day has come; we've finally entered the sandboxed era.

The plus side of sandboxing is that it means, in theory, that your apps will become safer and more trustworthy: Your Mac prevents them from accessing files they shouldn't access. But that security comes with a price, at least in some cases. Some developers say that --or, in some cases, to pull them from the Mac App Store entirely. For example, the sandbox generally prohibits actions like simulating key presses (like a typing expander tool might perform) or accessing root-level privileges (like executing certain command line scripts).

It's easy to see why the sandboxing requirement makes sense from Apple's perspective: For one thing, it's worked great on the iOS App Store. From day one, apps for the iPhone (and later iPad) were sharply limited as to what features and data they could access on those devices, and the result has been an impressive track record for iOS security.