# Error message versus warning, when problem is known

Consider the following MWE:

\documentclass{article}

\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
\coordinate (A) at (0,0);
\coordinate (B) at (1,0);
\coordinate (C) at ($(A)!.5!(B)$);
\end{tikzpicture}
\end{document}


./tikz.tex:11: Package tikz Error: You need to say \usetikzlibrary{calc} for
coordinate calculation.


As TikZ already knows that I am missing that one library, what is the advantage of giving this error rather than doing an implicit \usetikzlibrary{calc} and saying

Package tikz Warning: Automatically imported calc library as you are using