Hello @Adrian Chirtoc !
The benefit of Hybrid AD Join relies mostly on clients you are correct
The reason is the ability to provide Single Sign On , and only if your users are accesing the Servers to perform certain tasks , it is worth it to make them Hybrid AD Joined
Beside this scenario (rare) there is no other true benefit
From my experience we move Servers to the Cloud as Azure VMs , saving Datacenter costs and thats it! Maybe leave one or two Domain Controllers and if needed some specific Servers but we do not make them Hybrid AD Join , there is no reason !
I hope this helps!
Kindly mark the answer as Accepted and Upvote in case it helped!