  We review the appearance of the Planckian time $\tau_\text{Pl} = \hbar/(k_B
T)$ in both conventional and unconventional metals. We give a pedagogical
discussion of the various different timescales (quasiparticle, transport,
many-body) that characterize metals, emphasizing conditions under which these
times are the same or different. Throughout, we have attempted to clear up
aspects of the problem that had been confusing us, in the hope that this helps
the reader as well. We discuss the possibility of a Planckian bound on
dissipation from both a quasiparticle and a many-body perspective. Planckian
quasiparticles can arise naturally from a combination of inelastic scattering
and mass renormalization. Many-body dynamics, on the other hand, is constrained
by the basic time- and length- scales of local thermalization.
