Would you mind recommending a resource/article/wiki that goes into a but more detail on the 'Apply' menu? I understand how it relates to the Array modifier but are there other cases where 'Apply' comes in handy? What are the best practices.
Don't unless you absolutely have to. The point of modifiers is to make things quick and easy to modify. When you apply you lose that functionality. Which leads to slower workflow and more mistakes.
So "Apply" is basically like the "Reset X-form" tool in 3ds Max? (But in a more elegant way cause you can do it to Movement, Scale and Rotation independently from each other?)