This was my understanding. You basically get the gov't to pay for your clearance (which I hear can take a long time). Once you separate, your clearance can get your jobs in the private sector that people without clearance can't.[1]

I'm not saying it's a ticket to being filthy rich, but it opens doors to some lucrative careers that you wouldn't otherwise be able to get.

[1]https://www.clearancejobs.com/