Open source software is the most important thing for your computer. It means you have full control over all of the data on your computer. Linux (and other less popular open source operating systems) offers this control, where Windows and Mac OS and iOS emphatically DO NOT give you this control.
Why is this important? The simplest example I can think of is this: lets say you make a photo album on Pinterest or Facebook, or perhaps made with some fancy, easy-to-use software on your Windows computer. Ten or fifteen years from now, chances are you will not be able to get those picture back. On the social network, those photos will be buried by thousands of more recent photos. Even if you can find them, how long will it take for you to move those photos to another application? Will you have to click on each one, copy or download it, and paste or re-upload it? How long will it take for you to do that with 15 years of photos?
The album you made and saved to your Windows computer's hard drive or iPhone (unless it is a PDF file) will be useless because three PC's and how many smart phones later, the software you used to make it no longer exists, and you have nothing with which to view the files. All your photos will be trapped in that data file that doesn't open no matter how many times you click it. And unless you are rigorous in keeping your paper-printed photos, you will wonder why so few photos of your youth survive today.
What happened to that software? Well, maybe the software is owned by some brainless company that cares more about their bottom line than keeping you happy, especially if you haven't been buying all of their latest software and keeping your files up to date. Or maybe that software was intellectual property that was bought out by some other company who decided it wasn't a profitable product line and they no longer make newer versions for newer computers and smart phones. Or maybe you changed from iPhone to a Windows Mobile device, and the software you used to make it doesn't have version for your newest smart phone.
With open source, you are always guaranteed to have this data, regardless of the software you use in the future. Instead of printing everything, keep backups on an external hard drive, and you will be able to view, edit, and share the data you create forever. Open software isn't owned by some brainless company, it is just out there on the Internet, waiting to be downloaded and use by anyone who is interested. Your data isn't trapped in some social network, where the only way to view or edit that data is by clicking on every single one. The data is right there on your computer in a file you can view, edit, and share.
This goes for more than just photos. It goes for movies, stories you wrote, presentations, spread sheets, anything that is your data.
Why not just keep buying Microsoft Office or Adobe Photoshop? Well, consider how much these software packages cost (hundreds, sometimes thousands of dollars) compared to open source software (most of which is completely free). What sense does it make to pay full price for every new release, or for ever new computer you buy? What happens if you decide it's not worth the cost anymore? What will happen to your data when you stop paying for every new version of the software that made that data?
Please realize that if the digital data they create is important to you, open source is the only way to guarantee it will always work without paying continuously for upgrade to the software that created it. Think ahead, open source is the only way to go.