great question, i did not thinked about it yet but i can do a freemium saas,

let's say you can find users in same subject / goal as you and if you want to use its full potential you have to subscribe.

i can think of a calendar integration, maybe a video call, a reminder, a todo list with alert ( you get alert to remind you have this task to do), probably getting your partner's advancement into his goals in real time etc...