Ospf area design for back to back links

Hello, i would like to start some talk about ospf design for back to back links of branches.

If you have 2 branch routers connected to the the wan (area 0) and the branch network (area 100) What are the benefits for putting the b2b link of the branch routers into area 100?

As for my understanding it would be better if there are subnets that are not redundant to to the branch routers. So there will be network lsa for them between the routers.

But if there isnt, s summary lsa would be enough? As the b2b link would only be usefull if one wan link goes down.