The individual perspective is irrelevant. If the rest of the world was closed source, releasing your program open source wouldn't make much difference.

The difference is collectivization. When practiced widely, open source hardware means that you can find other designs that have tackled problems you've encountered. You can borrow one guys power block, find an audio block that meets your constraints, tack on a core complex from another project, and use a motor control from a fourth. You probably won't have anything to contribute to any of these projects: you may face some challenges they face, but collaborating with them is way harder than with software. That's ok. There's still a growing of a collective body of knowledge that others can recycle, and grow atop of. Open source hardware still does what is important about open source software: it empowers individuals to explore realms they would never have gotten to meddle with before.

As a small company, you can find a lot better a base than what you might develop in house if others are practicing open source hardware. And that means better kit for everyone.