I have this two simple images:
\documentclass{report}
\usepackage{tikz}
\begin{document}
\fbox{\tikz{%
\fill[red!20] (0,0) to[in=210,out=30] (10,0) -- (10,1) -- (0,1) -- cycle;
}}
\bigskip
\fbox{\tikz{%
\fill[red!20] (0,0) -- (10,0) -- (10,1) -- (0,1) -- cycle;
}}
\end{document}
And I am quite surprised about the bounding box of the first one:

Is it possible to achieve (automatically) tighter bounding box when using to[in=..., out=...] construct?