Strictly a matter of personal preference and your planned use. If you will have others traveling with you - kids or friends - then yes, it is ofetn convenient to have a bathroom that is separate from the master bedroom, either closed off by a separate door or located at the other end of the RV. If it's just you and your partner, it's probably most convenient to have the bath adjacent to or right in the bedroom.
Ya pays yur money and ya takes your choice...