Teams are not equivalent in the big or medium org. Some teams are pushing the boundaries (for the corp), some teams are doing grunt work, some teams are doing maintenance, some teams are support for all of those etc. Example - in our company it is often a case when a junior is hired to do lab support or general support, then transitions to a QA team for example, or a junior QA is hired to a steady working team and then transitions to a team doing fire requests and more visible stuff. In the process he acquires both general seniority and a lot of hands on domain knowledge which is complex in our case. Hiring a senior often means skipping only seniority growth, while he still needs a lot time to learn the domain and local quirks. I assume that averaged over years, juniors are still valuable par cost spent. Plus, juniors are sourced from the different pool of people than seniors, meaning more opportunities for a good hire.