  We revisit the standard argument to estimate the scale of new physics (NP)
beyond the SM, based on the sensitivity of the Higgs mass to quadratic
divergences. Although this argument is arguably naive, the corresponding
estimate, Lambda_SM < 2-3 TeV, works reasonably well in most cases and should
be considered a conservative bound, as it ignores other contributions to the
Higgs mass which are potentially large. Besides, the possibility of an
accidental Veltman-like cancellation does not raise significantly Lambda_SM.
One can obtain more precise implications from fine-tuning arguments in specific
examples of NP. Here we consider SUSY and right-handed (seesaw) neutrinos. SUSY
is a typical example for which the previous general estimate is indeed
conservative: the MSSM is fine-tuned a few %, even for soft masses of a few
hundred GeV. In contrast, other SUSY scenarios, in particular those with
low-scale SUSY breaking, can easily saturate the general bound on Lambda_SM.
The seesaw mechanism requires large fine-tuning if M_R > 10^7 GeV, unless there
is additional NP (SUSY being a favourite option).
