What is source code?
The most important advantage of open source is the possibility to access the application's source code, which in practice means having access to the code that is the result of the developer's work.
WHAT ARE THE BENEFITS OF HAVING ACCESS TO THE SOURCE CODE AND THE POSSIBILITY OF ITS MODIFICATION?
Access to the source code and its modifications provide the organization with unlimited possibilities to customize the application to the processes. At the same time, all resources and time invested in the software will remain in the company, and even changing the provider or the internal implementation team won't affect the added value of the software.
Thanks to having access to the source code, we can automate security [by performing a static code analysis] or perform a full security audit in accordance with OWASP ASVS, which would be impossible if we couldn't review the application's code.