[lvillani]

Another reason could be to ensure that you have at most one copy of the application ever, since you can force it to install stuff always at the same location.

On an unrelated product we learned that users ended up with many different copies of the app scattered throughout the system, if they were allowed to use the traditional bundle + DMG distribution method. Spotlight would then helpfully pick one random copy, with obvious consequences wrt. project file versioning. That is despite the DMG having the usual symlink to /Applications for a drag-and-drop installation.

[jcelerier]

yes, it's a total pain. users send you a crash log, you see that they're on an old version, ask them to update. They say they do, you get the next crash log, and it's still the old version. And then you get a screenshot and you see 12 different versions of your .app, in the desktop, in ~/Applications, in /Applications...

[nathancahill]

Even worse when they don't copy it off the DMG. Just leave the DMG mounted.. forever.

[AnIdiotOnTheNet]

Maybe, but that's also an advantage. Often it is useful to have two versions of the same application available, for example if you are testing one of them, or if a feature or compatibility was broken somewhere along the way. Typical package manager software installation does not accommodate such use cases.