Established codebase
The first lines of source code were added to GNU sed in 2004. This is a relatively long time for an open source project to stay active, and can be a very good sign.
A long source control history like this one shows that the project has enough merit to hold contributors's interest for a long time. It might indicate a mature and relatively bug-free code base, and can be a sign of an organized, dedicated development team.
Note: The source code for GNU sed might actually be older than the source control history can reveal. Many projects begin by duplicating a large amount of source code from an existing, older project. You can usually tell whether this is the case by looking for a rapid rise in the amount of code early in the project's history.