While I don't often switch avatars, it can be a pain to switch to a new avatar and then return to my main avatar only to re-calibrate my FBT back to what I had before. I say sometimes, because when trying out an avatar in an avatar world, I can go back to my previous avatar and the calibration settings remain the same; but only if I didn't calibrate to the "new" avatar I'm trying out. So that data is retained SOMEWHERE before re-calibrating.

Since most players don't alter their FBT setup during game play, it should be possible to retain that calibration data for an avatar you've already used; specifically avatars you've created and or have as a favorite. And if they did change their FBT setup during game play, they can re-calibrate using the calibrate button in the menu. Would it be a pain to calibrate multiple avatars you wanted to use for the day? Yes, but if implemented, you could calibrate the avatars once and switch to your heart's content, just like when playing without FBT.

Granted, I do see something like this becoming a memory-leak in the sense that some people like going through hundreds of avatars a day just to try them out. But if there was a limit set to a certain number of avatars (like a history that only retains X-number of avatars), or restricting it to favorites and uploaded ones, I don't foresee a possible memory-leak being a concern.