Is there any advantages by writing your code from scratch, besides that you know your application inside out? Which you also can with a framework developed application by actually reading the pre-made functions and methods you use.
It's a project manager nightmare.
Here's the answer I typically say.
If you are the only developer and only future maintainer of the codebase, go ahead and write your own framework. You will learn a lot, appreciate what other framework creators have done, and have an efficient system that ONLY does what it was supposed to do.
If there is any possibility that someone else might work on the codebase, do not write your own, unless you are willing to fully document every design decision from naming conventions to directory layouts to api design. Documenting is also a form of justification for your decisions, other devs might not agree with your choices or the current/future problem at hand is different then the architecture present.
Using a good framework( good meaning frequent releases, decent documentation, open project examples, an active community, and non-restrictive license (MIT/BSD)) is going to benefit you in the long term. Framework creators understand they are going to put together a set of tools that are going to be used for a variety of purposes, not a single solution to one problem. Your investment in the learning curve of the framework will pay off greatly the next time you use it.
If someone else has to work on your code, you shouldn't have to explain where everything is, just point them to the framework documentation. Hopefully hundreds or thousands of others have built applications and provided feedback to the creators about security/performance issues.
A good framework is easily extensible and plays well with existing class libraries. Many contributions from the community might provide partial solutions to your problem.
Most of the arguments against frameworks is the performance issue but in the vast majority of cases, caching will solve this issue. Footprint is another minor point but really, is there really a problem with a framework that is 500KB vs 2MB vs 8 MB? It is not like every file of the framework is included in a single php file.
As for the framework fanboys spouting off on which one is better, ignore. Every developer has his own style just like food preference, just pick a framework where you think your style best fits.