Re: Not in IT...
Call it what you like, Corporate knowledge, institutional experience it is invaluable when wrangling multiple services to work together.
Once you have outsourced your knowledge you are both unable to hold the supplier to account (because you have no idea what they should be doing), and unable to replace suppliers as the existing supplier then has to hand over, to a competitor(which they will either refuse or make extraordinarily expensive. Outsource capacity not capability!
Many firms rely on at least some home-brewed IT services to be competitive or some unique capability to stand out. Any more than none, will require some embedded wrangler experience and is outsourced at the peril of the corporate boss that thinks its a good idea.
In my experience outsourcing has generally not been a net cost saving once you tot it up. It only provides buffers against volatile demand or fills in hard-to-find specific skills.