Cons of Method A:

1. pdfcrop takes a significant amount of time. For a web-based system, it really hurts a system performance.
2. pdfcrop cannot crop a valuable object when the object is surrounded by a non-white background. See the pdfcrop author's confirmation in question: pdfcrop fails to crop a PDF document with non-white background ^[1] for the details.

3. pdfcrop might produce a bad cropping as follows.

   input file to be cropped by pdfcrop:

   % cropped-n.tex
   \documentclass{minimal}
   \parindent=0pt
   \begin{document}
   $\displaystyle n$%
   \end{document}
   

   main input file:

   % comparator.tex
   \documentclass{minimal}
   \usepackage{graphicx}
   \begin{document}
   $\displaystyle n$ \includegraphics{cropped-n}
   \end{document}
   

   output: It is difficult for normal eyes to detect the defect unless we magnify it 6400 times that is the maximum magnification scale provided by Adobe Reader.

Pros of Method A:

1. As long as the valuable object is surrounded by a white background, pdfcrop can trim the excessive white spaces. Thus we don't need to specify manually and exactly a tight paper size in advance. Using pdfcrop is practically very useful when we don't know the tight paper size in advance because of glyph issues that exist such as in the following examples.

   % example-1.tex
   \documentclass{minimal}
   \usepackage{xcolor}
   \usepackage[a5paper]{geometry}
   \parindent=0bp
   \begin{document}
   $\displaystyle E=mc^2$
   \end{document}
   

   or

   % example-2.tex
   \documentclass{minimal}
   \usepackage{pstricks}
   \usepackage[a5paper]{geometry}
   \parindent=0bp
   \begin{document}
   \begin{pspicture}[showgrid](2,3)
   \end{pspicture}
   \end{document}
   

Cons of Method B:

1. We need to specify manually a paper size in advance. The paper size can be specified exactly if there is no glyph issue, otherwise we must find a padding constant manually by trial and error. Here are the workarounds for the examples given in Pros of Method A:

   % workaround-for-example-1.tex
   \documentclass{minimal}
   
   \newlength\Left
   \newlength\Right
   \newlength\Bottom
   \newlength\Top
   
   % there are 4 magic numbers obtained by trial & errors.
   \setlength{\Left}{-0.420bp}
   \setlength{\Right}{-0.945bp}
   \setlength{\Bottom}{0.093bp}
   \setlength{\Top}{0.155bp}
   
   \newsavebox\IBox
   \savebox\IBox
   {%
       \raisebox{\dimexpr\depth+\Bottom\relax}
       [\dimexpr\totalheight+\Bottom+\Top\relax]
       {\hspace\Left$\displaystyle E=mc^2$\hspace\Right}
   }   
   
   \paperwidth=\wd\IBox
   \paperheight=\ht\IBox
   \voffset=-1in
   \hoffset=-1in
   \topskip=0bp
   \special{papersize=\the\paperwidth,\the\paperheight}
   \parindent=0bp
   
   \begin{document}
   \usebox{\IBox}
   \end{document}
   

   and

   % workaround-for-example-2.tex
   \documentclass{minimal}
   \usepackage{pstricks}
   
   \newlength\padding
   \newlength\Width
   \newlength\Height
   
   % it is a magic number obtained by a trial and error.
   % it is not necessary to make it so tight because it will be set to 0 at the final.
   \setlength{\padding}{8.4bp}% set it to 0 if you turn off the grid.
   \setlength{\Width}{2cm}
   \setlength{\Height}{3cm}    
   
   \paperwidth=\dimexpr2\padding+\Width\relax
   \paperheight=\dimexpr2\padding+\Height\relax
   \topskip=0bp
   \voffset=\dimexpr\padding-1in\relax
   \hoffset=\dimexpr\padding-1in\relax
   \special{papersize=\the\paperwidth,\the\paperheight}
   \parindent=0bp
   
   \begin{document}
   \begin{pspicture}[showgrid](\Width,\Height)
   \end{pspicture}
   \end{document
   

Pros of Method B:

1. Using the following batch file, we can compile workaround-for-example-1.tex and workaround-for-example-2.tex faster. We also don't need to specify too many switches such as embedding fonts, etc.

   rem simplified batch for method B.
   latex %1
   dvips -t unknown %1
   gswin32c -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=%1.pdf %1.ps 
   pdftops -eps %1.pdf
   

2. We can use \pagecolor{<non-white-color>}.

Summary

Good bye pdfcrop ...