Filtered colimits commute with forgetful functors

1) Let $T$ be a monad on a cocomplete category $C$. It is a general and trivial fact that the forgetful functor $\mathsf{Mod}(T) \to C$ preserves all colimits which $T$ presveres. In particular, if $T$ preserves filtered colimits (one then says that $T$ is finitary), then the forgetful functor does so. If $T$ is given by a theory of finite operations, $C$ has products which preserve filtered colimits in each variable, then $T$ is finitary.

2) Stalks of sheaves on $X$ commute with colimits because the stalk functor is left adjoint; in fact it is given by $i^*$ where $i : \{x\} \to X$, with right adjoint $i_*$.