Two Tight Ends
The Cleveland Browns could decide just to keep two tight ends on the week one 53 man roster. This would present itself in a way that Fannin is the backup to Njoku. The reason for this is you can't have too many two tight end packages if you only have two tight ends on the roster. If one of the two were to get injured in the first drive, you then lose a significant chunk of the playbook, this would be bad process.
Legitimate Depth
If they go ahead and sign a player like Jordan Akins then you can make the argument that the position room is perfectly set up to mix in plenty of two tight end packages. While Njoku is going to be more talented than the pair come week one, you feel confident if either of the other players are on the field. While people might assume Akins would be taking snaps from Fannin, he would actually open the door to more opportunities.
Some Depth
If they keep a depth player as tight end three like Blake Whiteheart, Brenden Bates or someone from waivers then it will likely mean Fannin is more covering when Njoku isn't on the field. There will be some crossover as they probably trend towards 1.2 tight ends per snap.
The one caveat to this is do they view Fannin as an interchangeable slot wide receiver instead. They could look to split these slot snaps between wide receivers and Fannin. When they need extra traditional tight end cover they might try Fannin but don't rule out someone else doing this role instead. Potentially a sixth offensive lineman if it is a heavy blocking role.