A Logic Layer is an overlay category which Subcompositions can be assigned to by using the Composition Navigator.
Subcompositions assigned to the same Logic Layer cannot be in their "In" state at the same time. If you send a Subcomposition to it's "In" state, any other Subcomposition assigned to the same Logic Layer will automatically be sent "Out". This is useful in avoiding Subcompositions from interfering with each-other On Air.
Logic Layer options in the Composition Navigator