  Recently there has been an interesting revival of the idea to use large extra
dimensions to address the dark energy problem, exploiting the (true)
observation that towers of states with masses split, by $M^2_N = f(N) m^2,$
with $f$ an unbounded function of the integer $N$, sometimes contribute to the
vacuum energy only an amount of order $m^D$ in $D$ dimensions. It has been
argued that this fact is a consequence of swampland conjectures and may require
a departure from Effective Field Theory (EFT) reasoning. We test this claim
with calculations for Casimir energies in extra dimensions. We show why the
domain of validity for EFTs ensures that the tower spacing scale $m$ is always
an upper bound on the UV scale for the lower-energy effective theory; use of an
EFT with a cutoff part way up a tower is not a controlled approximation. We
highlight the role played by the sometimes-suppressed contributions from towers
in extra-dimensional approaches to the cosmological constant problem, old and
new, and point out difficulties encountered in exploiting it. We compare recent
swampland realizations of these arguments with earlier approaches using
standard EFT examples, discussing successes and limitations of both.
