Before I go into the details of why an open-source CMS is a great option for your website lets first make sure we all understand what these terms mean.
CMS stands for content management system which is "a computer application that supports the creation and modification of digital content using a simple interface".
In other words, a program that makes it easier for non-developers to add content and make small changes to your website, examples include Wordpress, Joomla and Drupal.
Open Source can relate to anything that is created and then distributed freely, it also may be developed in a collaborative public manner.
Which means that people will normally upload software or code to a public repository like Github and then it is free for anyone to use, update and improve.
Put those two terms together and we get something amazing, a free application that makes it easier for any one to update your website whenever you need.
Why would we want to use these programs?
These are the reasons I think an open-source CMS is the best solution for developing a functional website:
Open Source is free
I think this is one of the best aspects of a CMS like Drupal, it is free and so are a most of the modules you can add to it for improvements or extra functionality.
That is pretty amazing in a world where everything is getting more and more expensive.
Open Source is frequently updated
As mentioned above open source is created and developed collaboratively which means that when bugs come up they can be fixed by anyone.
This allows for much quicker solutions than if it was just maintained by a single person or company.
Open Source has a community
Because so many people use open-source CMS' there is a large community for support.
There are thousands of websites, youtube channels and books out there dedicated to teaching people how to use these applications, which means that anything you need to know you can find online.
In conclusion, if you're looking to invest in a sustainable website that is highly customisable, and potentially much cheaper in the long run, I would look into an open-source CMS.