After thinking about it I can't come up with a good reason NOT to have a mic, even if it is never used. If something were to happen on the road and leave one in a state that they were only able to barely reach the phone button and barely speak it would still be possible to summon help if a phone was paired with it. My phone is paired to the Sena separately from the bike and it's in my jacket pocket zipped up, so I could still use it if necessary. And yes, there are plenty of places in the Hill Country in Texas where there is NO cell phone service of any kind, and yes, those are the most enjoyable roads to ride if for nothing else but the long views across the expanse of hills. You pays your money and you takes your chances. JMTCW, yours may differ.
Ride Safe!