Custom PHP/mySQL vs. Ruby on Rails

I am wondering what are the advantages / disadvantages of programming with Custom PHP code utilizing mySQL database verses using a framework like "Ruby on Rails".

I am not sure what the benefit is using a framework other than being able to program things "faster" once you're used to working in it.

But I feel as though I'm very fast and efficient with custom code and don't feel like I need a framework solution. I am very comfortable creating everything from "scratch" (I have tons of libraries of custom modules I've created and use all over the place). I have basically created my own framework just based on that it would seem.... 15 years of programming.

So, please tell me what is the real benefit of this. Main concern being, would it be much easier to scale the website as it grows using a framework? Or is it just a matter of more programming time.

Points to consider:
- Scalability
- Security
- Speed
- Programming Ease