  Most of the discussion regarding the Higgs boson couplings to Standard Model
vector bosons and fermions is presented with respect to what present and future
collider detectors will be able to measure. Here, we ask the more physics-based
question of how well do we need to measure the Higgs boson couplings? We first
present a reasonable definition of "need" and then investigate the answer in
the context of various highly motivated new physics scenarios: supersymmetry,
mixed-in hidden sector Higgs bosons, and a composite Higgs boson. We find the
largest coupling deviations away from the SM Higgs couplings that are possible
if no other state related to EWSB is directly accessible at the LHC. Depending
on the physics scenario under consideration, we find targets that range from
less than 1% to 10% for vector bosons, and from a few percent to tens of
percent for couplings to fermions.
