When more people work on different modules of a project its easy to introduce bugs concerning the interaction between these modules. Continuous integration addresses this problem by enforcing developers to at least commit once a day and then automatically run build and test scenarios. This won't prevent bugs but it makes it far easier to locate and fix them as the amount of new code is tiny compared to traditional (read rare) integrations of big pieces of new code. This approach minimizes the time needed to repair broken code and therefore allows you to concentrate on adding new features instead.
In order to take advantage of CI there are some requirements for the work flow of the team and the tools used. Firstly you need a continuous integration platform which allows you to automatically build and test your code base. Additionally there are some rules for the team to follow like not to check in code and going home without waiting for the result of the integration test or avoiding to check in when current build is broken. I guess this needs some time till this works flawlessly. Furthermore I don't don't think that is always possible to decompose a module into such small pieces so you can commit one a day. Then you again need a more substantial integration which is much more error prone.
I think continuous integration is a powerful concept to enhance software quality while reducing development time