Open source is so ubiquitous nowadays that its inevitable you are benefiting from it every day even if you don’t know it just by using applications on the desktop, web, or mobile. The applications you use most likely have dependencies that are open source. If you’re on Mac or Linux, the unix kernel that powers them is open source.
Many people including myself feel encouraged to contribute projects that we use and benefit from because it helps the ecosystem as a whole. The entire ecosystem grows exponentially as more people contribute and work together, it’s a powerful thing.