We can manage small applications in custom PHP but if the requirement is huge then we have to follow some framework. Codeigniter is one of the leading framework based on PHP. Its follow MVC Architecture.
Codeigniter has it’s own library so we will get help from existing class and objects. Also if a customer needs further enhancement then this framework will help a lot to other development team.
In custom PHP everyone follows their own coding structure. By using this types of framework you have to follow it’s own structure which is very useful to other development team.