You might carry your phone, but having an Elemnt or Elemnt Bolt wouldn't run down the phone battery the same way. In this regard, it wouldn't be that much different than just having your phone sitting on your desk while you are at work.

When I ride, the phone itself is in a pocket or pannier. Sometimes I run the wahoo app on the phone before starting the ride, sometimes I don't bother. But if I do have it running, I get caller-ID on the Bolt so I know if it is something I ought to stop and answer, or just another telemarketer. If I don't have the app running, I would hear the phone ringing, but not know who it is.

Before I got the Bolt, I had a RFLKT, and that thing was tethered to the phone and only acted as a remote display for the phone app. Thus if the phone battery went flat on a ride, the RFLKT would go blank as well. This won't happen with an Elemnt - it is autonomous - it can largely do everything without needing to be connected to the phone. If you wanted to change route in the middle of a ride, you would need to pull the phone out.