There is a common question that clicks to the minds of many people and you might also be brooding over it. The question is what the need of a plugin is when you can make changes in your functions.php file. Yes you can possibly do that as this file provides an opportunity for developers to add plugin like functionality without actually creating it.
Now there are two important reasons for choosing custom Plugin development over theme modification. Firstly everyone wants their website to be loosely coupled. Wrapping up a function into a package and keeping it different from others is always better. This offers a structured way to work without disturbing other elements. So if you choose to integrate a plugin you are opting for the loose coupling architecture.
The3 second important reason is that if you ask your developer to make changes in the functions.php, then these changes will not reflect as you switch themes. This can be a great disadvantage to you. A custom plug-in can be integrated irrespective of the theme that you are using.
So it is always good to get a custom plug-in instead of adding code into your functions.php file.
