As a freelancer and a small time publisher, I lack the skills of true game designers so I'd never qualify for working for any of the big game publishers, though I still have something to contribute. Had there not been an OGL, I don't think I'd ever have been able to participate as I have. As a cartographer, I mostly get commissions from 3PP companies, without an OGL there wouldn't be any 3PP companies. I have gotten a Paizo Publishing map commission once, and though they're a big one, Paizo was still a 3PP, until the creation of Pathfinder. So the OGL has been critical for all opportunities I've ever had to create artistic cartography for publishers in the industry.
Through 3PP connections, I've managed to get a personal homebrew setting developed with several authors, game designers, editors and 3PP owner/publisher, Steven Russell of Rite Publishing, as an imprint under his company. Since Steve is 3PP, his existence depended on the OGL, and wouldn't be available to me, if such didn't exist. I'd have never gotten my Kaidan setting of Japanese horror (PFRPG) off the ground had there not been an OGL.
So the OGL's existence, is everything to me. Without it, I'd only ever be a player and gamemaster, and not a low level participant in the RPG industry as I am today.