Look at this from a business's point of view, rather than a software developer.
Say I run a small business, perhaps a lawyer's office. No one in the company writes software. But my company needs a lot of software to make money. IT costs are a major issue for smaller companies, consider the basic infrastructure
- A PC of some kind for every employer, and the operating system for it
- An office suite (word processor, spreadsheet, and probably presentation software)
- File servers and some collaboration software.
- Other productivity software (time keeping, for example)
- Accounting and payroll systems
- Regular upgrades for all the software
Not that long ago, a new business had only one realistic option. The OS came with the computer, and everything else followed. But today there are widely used open source alternatives for everything in the list above. Even more interestingly, if it's a Linux based solution, you can often get away with lower spec'd (i.e. cheaper) PC's.
So going with Linux, Open/Libre Office, and other open source packages will save my company a lot of money each year. Possibly enough to hire another employee to help generate revenue. That's more jobs and more businesses feeding the economy. That may mean more clients and more revenue.
The biggest downside, of course, is the lack of a one-stop-support organization ... and anyone who's ever listened to the hold-jockeys at a certain company for hours can talk to you about just how well that works out.
The other is simply the difficulty for a non-savvy user to know which software to use, or even what exists.
But these actually open up scope for a new business: consultants who, for a fee, help set up the office for new businesses. They identify the right software, and set it up. They might even provide the ongoing support.
On a much smaller scale, my entire household is moving away from Windows to Macs as the old laptops die. I used to have multiple licenses of Office etc. Today, the only software I regularly buy is Turbotax once a year and every few years I update Quicken.
Apple doesn't even charge for major OS upgrades any more. And a Mac is close enough to Linux for me to be able to do full OS development on it with all my favorite libraries and tools.
My development desktop at work runs Ubuntu and there isn't a single piece of paid-for software on it. My employer has hundreds of these.