Yea good for people who are familiar with it and use it often. For me I use the tard alternative as it's most efficient, waste of time to learn something I'm hardly going to use. Takes me a few mins to scan and batch resize an entire tree of image files.
Imagemagick is a nice tool, specially when you're an opensource addict and have no tool to manipulate numerous images at a time (I don't know to translate "traitement par lot", which GIMP doesn't do). It's also handy when using shell script, for expl, you can easily make a script to build an HTML (or BBCode...) gallery with the images you just cropped/resized/converted/... . You don't have to learn everything, only the few parameters you need ;-) so it doesn't take that much time, and once you're aware of what that tool can do it can save you some time ; but I think it's mostly for linux users who are already a bit trained with shell scripts. I never really took the pain to learn windows scripting ...