While I am not a water quality expert, I can tell you that it is still possible to have sediment. I would recommend following the same maintenance routine you do for your hot water heater. If you prefer not to have to occasionally manually drain your generator, I would highly recommend the auto drain simply as added "insurance" for your generator's endurance. Read the response to a similar concern below.
Now water quality is
a factor for every steam generator out there. Poor water quality will eventually affect your generator's performance, even to the point of having to replace the generator. This is why all of the leading manufacturers offer drain systems for routine maintenance and have water quality recommendations. This is no different than with your hot water heater
If you have a water filter already installed, you are probably fine but I would recommend that you call a Steam Shower Specialist
to review your installation and verify your needs, if any.