Is quantum entanglement really needed?

On tuesday at UQ Carl Caves gave a Quantum Science Seminar "Quantum metrology meets Quantum Information Science".

One side point he made was that just because quantum entanglement is glamorous and beloved by luxury journals does not mean that you actually always need it to optimise any and every task. A specific example is in this paper which states:

The Heisenberg limit is thus achieved without any entanglement between the arms of the interferometer. In fact, Jiang, Lang, and Caves [4] showed that the state ∣∣ψin⟩optis the only nonclassical product state, i.e., not a coherent state, that produces no modal entanglement after a beam splitter. These results indicate that, as in Ref. [18], modal entanglement is not a crucial resource for quantum-enhanced interferometry.