hmm. i never really gave much attention to it but still it's good to know.

mostly debugging, it will allow you to see your errors, but it can also allow you to change values dyanmically so you can see the changes in game immediately.

Yeah, I have to say people seem to drastically under appreciate the Dev.exe, in addition to the aforementioned advantages, it has a huge number of very useful analysis tools, it's brilliant for checking the effects of changes on the AI, as well as everything from checking on mesh point errors to setting up specific scenarios for testing. To say nothing of the things about the inner workings of Sins you will learn from playing around with it. 

Alright, mini rant over