Many enterprise organizations have a build/deployment process that is archaic, error prone, and takes lots of time.(in terms of man hours, and deployment latency.) A build or release engineer comes in and takes that process and transforms it into the press of button. Basically just build/deployment automation.

But the benefits to an org are vast for just a couple of months of the build engineers time. -Deploys much faster deployment, shortening the feedback loop between end users and development -Is far less error prone. The manager doesn't have to explain to his boss why development started deploying last night at 6pm but now it's 10 am the next day and the software still doesn't work. -No longer has to pay someone to sit there and baby sits builds all the time.

I've worked with a couple of release experts and they've always been extremely valuable.

Not the original person, but in any organization with a non trivial amount of code needs someone that is really on top of managing how the applications build and how dependencies mesh together. There's many tools to learn and leverage (in java you have ant/ivy, maven, gradle) and can easily take up a fairly large amount of time to organize. If done properly it can also prevent certain project failure.