It depend on your likes and dislikes. If you like more bass and find your self boosting the lows when listening to music, then a Sub may be what you need.

If you leave the tone settings basically flat (like I do) then you may not need a sub.

One thing to nete: you can only pair a Sub to one set of speakers. So if you think you need a Sub on bot, especially if they are in different rooms, you will need two Subs.

Thanks. I did not know about the subwoofer being for just one set of speakers. It sounds great to me but I don’t have a sophisticated ear. 

You should also know that you can’t bond a sub to Move speakers.