Needed in order to do Kummer theory for \(p{\hbox{-}}\)torsion in characteristic \(p\), since the following SES is exact in fppf sheaves but not in etale sheaves: \begin{align*} 0\to \mu_p \to {\mathbf{G}}_m \xrightarrow{\cdot p} {\mathbf{G}}_m\to 0 \end{align*}