not all roles build equally useful networks. i was in, i dunno, "research aerospace" for 10+ years, and it was basically a waste from a networking standpoint. nearly everyone i knew there is either still in the same job, or retired. the handful of others that left aren't even in the same state any more.
i think the job did really profound damage to my career because of it. i think i'd encourage CS college grads to work 3-4 places before they're 30, and make sure all of them are places with at least a tiny bit of turn over. nowhere that has people trying to hit 30 years in the same chair to get a pension.