When should I use \psgraph instead of \pspicture plus \psaxes?

Question

I am new to PSTricks and want to plot some functions. The documentation of pst-plot explains (but not detailed enough) both \psgraph environment and the combination of \pspicture and \psaxes. The thing I want to know is:

When should I use one rather than the other one?

Bonus question: I want to change the font of the axis labels from text to math. How can we do that?

\documentclass{minimal}
\usepackage{pst-plot}

\begin{document}
\begin{psgraph}[]{->}(0,0)(-1,-2)(\psPiTwo,2){8cm}{6cm}
    % plotting 
\end{psgraph}
\end{document}

Output:

Answer 1

Since they are interchangeable, there should be no problem using either one or the other.

You should be able to change the x/y labels using

\psset[pst-plot]{xAxisLabel=$x$,yAxisLabel=$y$}

Here is a complete MWE:

\documentclass{article}
\usepackage{pst-plot}% http://ctan.org/pkg/pst-plot
\begin{document}
\psset[pst-plot]{xAxisLabel=$x$,yAxisLabel=$y$}
\begin{psgraph}[]{->}(0,0)(-1,-2)(\psPiTwo,2){8cm}{6cm}
    % plotting 
\end{psgraph}
\end{document}