What are some of the reasons to install multiple collectors?
1) better geographical coverage
2) increase the traffic capture bandwidth
3) offload log parsing
4) over...
MSPs have collectors installed on various customer's sites.
Collectors also act as a dependency so if a site goes down and takes the collectors down too, you don't get all the devices at that site to send tons of alert notifications.
Remote Access via collector proxy might help gain access if site-to-site connection is down.