In the case of the G5, if you don't install the software, you can still change DPI on-the-fly, but it is limited to the three default DPI settings. So if you want to change what those values are, and have up to 5 levels, you'll need to install Setpoint. Also would need Setpoint to customize buttons to specific functions and use profiles.
But Setpoint is a huge bloat, and that's being nice. You can find all of the older versions released. I use 3.1.