I've seen a number of really good retentions on the technical side, and meant billets that would have been empty otherwise (due to the person being in a front line job instead).
Wasn't NATO knee, but for some people MELs seems to be the only thing keeping them from jetty jumping (which can take a toll and lead to MELs).
For an organization that is short people, losing experience, and wants to rebuild, not retaining experienced people doesn't make sense, if they can still make a meaningful contribution. There is a hiring process where they can transfer to the public service, but its time consuming and actually increases the SWE. Case by case obviously, so your mileage will vary, but when we develop specialists with 20 years of experience and run a lot of obsolete kit, it's nuts.