Why use units of $\rm 1/Hz$ instead of $\rm s$? The Wikipedia page for Planck's constant frequently includes the constant in units $\text{J/Hz}$ or $\text{J} \times \text{Hz}^{-1}$. Is there a reason these units are used instead of $\text{J} \times \text{s}$?
https://en.wikipedia.org/wiki/Planck_constant
 A: The most common physical reason is that $E = hf$ relates the energy of a photon to its frequency. The frequency in SI units is given in Hz.
For a similar reason the Wikipedia provides the values of $hc$ in units of Joule-meter because $E = \frac{hc}{\lambda}$, in this case the wavelength $\lambda$ is often written in meters.
Lastly, you may wonder why units of $eV$ are sometimes used instead of Joules. For particle physics, doing calculations for single elementary charges and Volts is useful, hence the electron volt. And again we can understand this from the point of view of the photon, since photons with energy will interact with electrons in atoms on the eV scale (and electrons not in atoms, as well, for which the eV is a convenient unit). For example, ionizing a hydrogen atom requires a photon with energy 13.6 eV.
A: In addition to the other answer, the Wiki article you cited has (in accordance with NIST) the units $JHz^{-1}$, perhaps to distinguish it from the units used for the reduced Planck constant, $\hbar$ (see below distinction when using angular frequency).
We almost always use the reduced Planck constant $$\hbar=\frac{h}{2\pi}$$ in physical calculations. For example, we write energy as $$E=\hbar\omega$$ where $\omega=2\pi f$ $\text{radians s}^{-1}$
By definition, the unit $Hz$ is strictly cycles per second. But because we have divided Planck's constant by the factor $2\pi$ we have switched from normal frequency, which has units $Hz$ and reduced it to $\hbar$ that should now be used in conjunction with radians, everywhere it is used. But since radians are dimensionless, we must use $Js$. Hence $h$ would have units $JHz^{-1}$ but the reduced Planck constant, which is ubiquitous in quantum physics, $\hbar$ must have units $Js$.
