Want My Life Back on "BEC Written Communication... BEC Topics only? Or are all fair game?"

So, I'm a little confused.

For the BEC Written Communication, will the written communication be on BEC related topics only?
Or are all topics fair game?
(For example, could they ask you to write a memo to advise a tax client, etc..)

Everyone I ask gives me a different answer, so I am asking the experts!

Thanks!