\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{showgrid}
%\tikzset{showgrid} % would enable it globally
\tikzset{every show grid/.style={show grid/keep bb}}%  Keep the original bounding box!
\begin{document}
\noindent
\begin{tikzpicture}
    \draw (3,2) -- +(45:3);
\end{tikzpicture}
\hspace{1cm}%
\begin{tikzpicture}[show grid=false]
    \draw (3,2) -- +(45:3);
\end{tikzpicture}
\hspace{1cm}%
\begin{tikzpicture}[show grid]
    \draw (3,2) -- +(45:3);
\end{tikzpicture}
\hspace{1cm}%
\begin{tikzpicture}[show grid=true]
    \draw (3,2) -- +(45:3);
\end{tikzpicture}
\par\bigskip\bigskip\bigskip\noindent
\begin{tikzpicture}[show grid=left]
    \draw (3,2) -- +(45:3);
\end{tikzpicture}
\hspace{1cm}%
\begin{tikzpicture}[show grid=right]
    \draw (3,2) -- +(45:3);
\end{tikzpicture}
\hspace{1cm}%
\begin{tikzpicture}[show grid=above]
    \draw (3,2) -- +(45:3);
\end{tikzpicture}
\hspace{1cm}%
\begin{tikzpicture}[show grid=below]
    \draw (3,2) -- +(45:3);
\end{tikzpicture}
\par\bigskip\bigskip\bigskip\noindent
\begin{tikzpicture}[show grid={left,right}]
    \draw (3,2) -- +(45:3);
\end{tikzpicture}
\hspace{1cm}%
\begin{tikzpicture}[show grid={right,above}]
    \draw (3,2) -- +(45:3);
\end{tikzpicture}
\hspace{1cm}%
\begin{tikzpicture}[show grid={above,below}]
    \draw (3,2) -- +(45:3);
\end{tikzpicture}
\hspace{1cm}%
\begin{tikzpicture}[show grid={below,right}]
    \draw (3,2) -- +(45:3);
\end{tikzpicture}
\end{document}