We usually recommend selecting 6-8 monitoring locations for each of your monitored website or service. These are more than enough to determine whether or not your website/service is experiencing a downtime.
As explained in this documentation article (link), our system checks from all of the selected locations simultaneously, so you should be cautious not to select too many locations per monitored website/service, as to not overload it, or get our monitoring IPs blocked in the server’s firewall (which can then generate false positives for your monitors).
We offer multiple locations, so you have options to choose from, and not necessarily to select all of these for each of your uptime monitor.