The experience you get in open source and being able to talk about it in interviews can really help once you get there, but it doesn't help get the interview and you have to really apply yourself to get something valuable out of it. My GitHub CV is full of a bunch of bullshit I started and spent at most a month on before abandoning. Of course I've worked on a project for two years now and I wasn't even allowed to include it because there's no boss or company or address - just me and another guy from Europe I met online working on a passion project that probably neither of us have the drive to turn into a business.