Disabling Multi-Band may cause the device to track more Galileo satellites, but even then only a maximum of twelve signal bars will be displayed across the screen, the same number of signals being tracking with Multi-Band enabled in the example above.
The number of tracked satellite signals depends on multiple factors, primarily the number of satellite signals available at any given time and location for the desired constellation. Trimble GNSS Planning is one of our favorite methods for viewing satellite constellation availability.
Additionally, it has been observed by many users that using 'GPS Only' frequently provides better accuracy than when using 'GPS + GLONASS'. The only reason we would enable 'GPS+GLONASS' on our Garmin devices would be if there were an insufficient number of 'GPS Only' satellite signals available and 'GPS + Galileo' was not an available option.