That is a way to inform newcomers and interested people (who visit the project page from time to time, or subscribe to the ‘News’ RSS feed) about a major change or event within the project.
You can also setup news entries to be sent to a mailing list (that’s possible for the other trackers as well).
The purpose of this feature is informational—if members need to know about an important change (in practices, procedures, etc.), it is perfectly OK to announce it here. Some teams use it to announce new translations, which is also fine.