It isn't mandatory but it is definitely recommended. Especially from yobit, since they're known for issues/extreme delay with swaps/upgrading wallets/etc.
Just keep you Espers on your desktop wallet and wait for the news of coin swapping, as the Dev said already before, coin swapping will be done through exchanges thats the reason that they are contacting them as well, so I am thinking it will be automatic once you got your coins on the exchange... so right now its best to pull them out especially from those exchanges that are experiencing withdrawal issues like novaexchange at the moment and yobit which might just hit a problem.