It makes your serfdom in modern technofeudalism less geographically restricted. Makes you more free for some definitions of "free".
I struggled less to relocate from France to China than I did to relocate from France to Germany.
Like everything in Europe, on paper it’s good, in reality, it’s often mediocre. Sad thing.
We might want to throw in cross border workers (frontaliers/Grenzgänger). That's a bit different. It can be very interesting financially even on the lower end of salary or qualifications. But that possibility existed before the EU and won't disappear after the EU.
From what I heard, I need to rent apartment, do anmeldung, set up bank account, buy health insurance, pay monthly tv fee, register for taxes and file them every year. Then I hope to live without worries.
Remember that legal, economic immigration in Europe is possible without Schengen style free movement. It really wasn't that hard before.
I'm willing to study facts (numbers) that prove the benefit of free movement but they would have to show that legal, economic immigration without Schengen doesn't bring the same benefit. And legal, economic immigration without Schengen seems to have a lot less disadvantages.