I like taking part in the community. It makes me feel like I am part of something. A truly great, modern something. Jupitercow has been great for this, and we see it as important to make publicly available, at least some, of our new ideas to help give back to a community that has helped build this business over the past decade.
If I am being honest, though, the greatest reason to release as much as we can into the community for free is somewhat selfish: We get some truly excellent feedback from the community that makes our software so much stronger and much more versatile.
When we took over development for an out of date plugin that worked with Gravity Forms to allow users to update existing posts through a contact form, we did so because the pre existing version was not being updated or supported. We rewrote that almost from the ground up to create a plugin that started to really fill the need we had for it. However, once we released that plugin publicly, and even more so once we added it to the WordPress Plugin Repository, it has really become a great plugin.
The ideas and bugs found by the community so far, have been a huge help in making the plugin something that fits most use cases we through at it and is a much more solid experience.
The best thing about open source is that the people who use your application strengthen it every chance they get. If your code sits on a client site or two without taking advantage of what the community has to offer, you are missing out on a lot, and likely so is everyone else.