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Personally I think it's a very useful feature: the purpose for running which may not be to get the full path to the executable and then run it, but rather that that path prefix is important for something else. I'm sure when I joined this issue I had some need like that -- after all, as you say, if you just want to run it then there are better ways.
In general, once users have a need (for whatever reason) to start firing off subprocesses from their Python scripts, things can get ugly. Providing a portable path search function provides a way to keep one kind of that ugliness inside Python for the cases where it really is needed. As for abuse... well, people will always find a way to abuse bits of the library: I think that's an issue for them, rather than a reason to block this functionality ;)
My 0ドル.02,
Andy