You catch build breaks early on.
In a distributed development environment where developers do not always communicate with one another, continuous integration is a great way to assure the developer that the build he or she is building is the latest one.
Continuous integration also causes less regression
The feedback loop is smaller.
A developer does not have to wait for the end of the day or week to find out how the check-in affected the build.
Integration testing moves up in the chain.
Every check-in goes through the integration testing where problems are caught early.
Continuous integration enforces better development processes.
Each developer is held accountable.
You always have a latest-and-greatest build to use in demos, showcases, etc.