Well, Schengen brings open borders and tax-free trade.
Meaning when I’m traveling from Croatia to UK I need only ID card and not passport anymore, there is no border if you go with car to Italy/Austria, just drive trough.
For example before I can buy something in Italy/Austria only up to 150Eur / person, all above I need to go to customs, pay tax etc, or I’m smuggler if I don’t do.
If my company buys something in Austria, i don’t need to pay VAT in my country.
There is no 3 months limit anymore for me to stay in any EU country, I can stay there as long as I like, and depending on country I can apply for any job just like i’m local, I don’t need a special invitation, proof or other tons of paper.
That’s what’s all about.
Right now, there are some more border controls because of immigrants, and bomb attacks around the Europe.