The Dev.exe is a way to create mods and to figure out what is wrong with the mod.
It is basically the same as the game, but you can basically can most part of the game mod, and
if you changed a file during the game, the game would automaically reload the file and then would apply the changes, unlike the game, if you change something in a mod, you need to restart. This will only occur if you change a none significant entity file, however, if you change some thing that will change the interface, or meshes you will defintely restart just to see the changes
PS: just a word, it will reset the setting.settings in your settings folder