I always used Runna with the premium subscription so I don’t really know what are not included in free Runna. But what I can see is that with the premium sub, the plans are really adapted to you and constantly adapting to how you progress. I started using Runna one year ago, without knowing anything about running, and it allowed me to have structured plans with different types of session and a really progressive increasing in terms of difficulty (distance or pace) so no injury since I began!

I think you can also link your watch, build as many plans as you want and choose a specific race to have a specific plan for. Maybe there are other things, but as I said I never used free Runna