With the preamp gain, the operating system (Windows, OSX etc) can control it using the OS's volume control. However, sometimes when you reconnect the device the operating system ignores the existing gain setting and overrides it with the last gain setting you used on that computer. So, if you use the i2M editor to set the gain, the next time you connect to the computer, it will change it without you realising. The OS shouldn't do this if it fully follows the USB Audio specs, but unfortunately subtle details like this are often ignored.
So, we added an "exclusive" option that prevents the OS volume control being able to control the gain, and you have to do it through the i2M editor instead. If you're using the editor, I would recommend enabling exclusive so you always know what the gain is set to.