This is a somewhat subjective question, but I suspect that it might have a satisfying answer, so I'm going to ask anyway.
LaTeX is a tool for typesetting text. There are lots of packages, such as TikZ and pgf, which permit a user to produce graphical elements inside of a LaTeX document. On the other hand, you could create all your graphics with an external program, and include it in the document in an appropriate way.
There are certain situations where it is obvious to use an external program (a complicated plot or a photograph, for instance). And there are certain cases where you really should use something compatible with LaTeX, for instance if your images need to be typeset alongside text in some way which is not possible by simply including the image directly in the document.
My question is: as an experienced TeX user, how should you decide when to use a LaTeX package versus an external tool for creating graphics? This is obviously subjective, and it depends on your particular application. But what properties of your application should you consider when deciding whether an image is suitable or unsuitable for production in LaTeX?
Again, this is an obviously subjective question - but I suspect that there may be an answer which is mostly in 'the spirit' of what LaTeX is 'meant to do'.
