It has greatly reduced cost of border control as internal borders within the Schengen Area no longer have to be patrolled. Also, all members share in the cost of maintaining external border controls, so small countries on the edge of the Schengen Area don't shoulder a disproportionate cost.The downside to this is that some countries are more lax about their border control than others, which might allow people into countries that don't want them.2. It has greatly reduced the time it takes to move goods across Europe. It the past, it could take hours for trucks to cross certain borders, now the border may go completely unnoticed. This makes it much easier, quicker, and cheaper to move goods around Europe.The downside (depending on who you are), the reduced wait times at border crossings devastated the prostitution industry along the Germany-Czech border. Previously, truckers who often had to wait hours at the border, would take advantage of the services prostitutes had to offer. Now truckers have no reason to stop there.3. A common visa policy across Europe makes it much easier for foreigners to figure out what they need to do to get a visa. Also, it allows for some interesting visa arrangements. I spent some time in Estonia which doesn't have embassies or consulates in many developing countries. Students from such countries could get visas from any other Schengen member and still be allowed to stay in Estonia.The downside is that once their visa expires, the person has to leave the entire Schengen Area and can't just go to another country within the Schengen Area.4. It allows people to move freely around Europe. Without internal border controls, people are free to travel wherever they wish within the Schengen Area without having to worry about passports, visas, and long lines at control points.The downside is that some people don't necessarily want to allow everyone into their country with little to no scrutiny.