No, you don't have to plan anything if you don't want to. You can activate the pass with an empty My Trip. You can add journeys as you travel, you can remove journeys if you change plans etc. In terms of flexibility, there's no difference between paper and mobile pass.

Thank you, but still confused . In FAQ's , there is (Q) Can I change the trip connected to my pass ? (A) You can change the trip your pass is connected you until you activate your pass. Once your pass is activated , you can't disconnect a trip or connect a different trip .  I don't understand what this means.

This "trip” will eventually contain all journeys you make during the validity of your pass. But you don't have to plan any of these journeys in advance and you can change them if you like. It's just that, during the activation, you create a trip and give it a name and that trip will have to stay connected to your pass. But you can still freely change the contents of your trip (the journeys).