If your topic is in the news regularly for example, you'd probably want to know about new developments as soon as possible. In that case a search engine could help. Google is just one of them.
Google Alerts are email updates of the latest relevant Google results (web, news, etc.) based on your choice of query or topic.
Some handy uses of Google Alerts include:
- Monitoring a developing news story
- Keeping current on a competitor or industry
- Getting the latest on a celebrity or event
- Keeping tabs on your favorite sports teams
Source: http://www.google.com/alerts