By default, every Windows computer in your organization keeps its own local event logs. You examined these logs in the Searching event logs for specific events recipe. The logs on SRV1, for example, are separate from the logs on DC1. In larger environments, analyzing event logs across large number of servers is complex. With 100 servers, you would need to run a script on each of those 100 servers, which could become quite complex. Having each server forward events to a central computer can simplify this task greatly.
Also consider what happens if a server is compromised. Hackers often clear event logs after doing naughty things on a hacked machine. This helps to cover the hacker's tracks. A best security practice is to get the event details sent to a central and hopefully more secure server as quickly as possible. With Windows, you can...