My experience: Went to work at a startup transitioning to the next stage. When hired I was told everything is available to all employees, 'there are no secrets here'. I quickly found that most was locked away...and then noticed the same in many places. That and what comes with it led to my leaving. When I left I went back for a pseudo-exit interview with the CEO and he actually told me he had been screwing my team for the past year. In essence what I found was mostly lies. The lies began in interview (everything open to everyone) and continued until I left (continuing to hire based on things that don't exist at the company...like HR). My take: if you are told one thing and find it different, look around at more things.
Where I am at now we can see all the repos for all projects in the company regardless of team. The only pre-req is to be added to the company's github organization. We have a lot of cross team work, though, and I have worked on a few services that aren't related to my team and it would be a pain to have to request access.
At my last job, however, everything was locked down and you had to request access to just about every repo. It was a pain in the ass and there was no real valid reason to do so.