That should work, the script is probably done so that it uses lat/lon as long as they are provided, if not, it tries to auto-locate you using the IP and if that fails as well (you can reject the permission to geolocate you) then they have one default location for everyone. This is how it is normally done and I use this too, basically you have 3 possibilities in the following precedence:
1. try using lat/lon if provided in URL
2. if not, try to geolocate the person using IP
3. if location is still N/A use some default co-ordinates hard-coded in the code