Differences between frameworks are not just personal ones, , just go to this link below and see that there are yes, technical differences between them, differences, which may bring more application.
link
For example:
CodeIgniter does not have native support for ajax, authentication modules, event-driven programming, and CakePhp has all this, but it does not have native templates.
These are technical differences, depending on your team or your knowledge, will make a difference during development, so you need to do a good survey of requirements for your project to make a good choice. >
In which case you can use 2 frameworks:
For example, you build an application, and want to give it another interface, such as REST, you could use one framework to manage the application's online site and another to give REST access, with totally different business rules, some frameworks can do everything, others do not.
But between us, what would be the benefit of this, considering that you will have to rewrite rules, validations, business models, to use a single database.
Cases in which it is useful and common to marry more than one framework: Different technologies
PHP Framework + Database abstraction, example: Doctrine.
PHP Framework + Frontend Framework, example: Bootstrap, foundation, 960gs, etc.