The often overlooked benefit in data hiding or encapsulation is that objects are a whole lot easier to debug than are big gloppy strands of spaghetti code referring to the member variables of hundreds of classes. For example if you know that only way a variable can change is by way of an accessor function, then you can set a breakpoint at that function. Each time the breakpoint is taken it's a simple matter of examining the call stack and finding out why the variable was being changed.

One of the problems I run into a lot these days is people who could think in an object oriented fashion. If a developer can not figure out a reason to hide the data, then it's probably not a good class of candidate, period.

Don't make a class out a group of related variables just because you can! It's just a structure or a map or a collection. It's not an object, ok? Objects handle all of their own member manipulation. This includes reading them from a database, writing them to a database, displaying them in a dialog box, performing complex calculations involving the data, etc.