Codeigniter Benefits
MVC System (Model-View-Controlle) - Allows a separation between logic and presentation. The Model communicates with the database, the view, is how the application is presented to the user and the controlle makes the connection between model and view, also processes HTTP requests to generate pages.
Form Validation - Uses an effective validation framework system so that writing codes in single lines is possible. The framework generates error free codes.
Easy configuration and customization - allows you to configure the various aspects according to the web application. Also, CodeIgniter allows the easy editing of existing files;
Error Handling - The interfaces available lets you find error functions present in the application;
Database Integration - databases like PostgreSQL or MySQL come with CodeIgniter by default. If you want to use a database like Mongo, then you have to third party libraries for it.