Pat, we were in large plaza in France filled with tourists, locals, baby strollers, dogs, etc, maybe a couple of hundred. We had just enter from one side intending to cross to the other side when we became aware of a large amount of noise, confusion, shrill whistles, and heavily armed, soldiers with black face masks running toward us. There was a half dozen military transports in the street with soldiers jumping out of the back of the last two or three. Look liked a flying wedge of troops down the middle separated the people into two groups and forcing them back against the buildings surrounding the plaza. In a matter of a couple of minutes they had two large of people surrounded and pinned about the store fronts. They were shouting something in French but we noticed that people were pulling out passports, showing them to about every four or fifth soldier on the perimeter and they were then being allowed to pass through the line. We did the same, he looked at the passport picture, then at us, and then said, I think, sorti, sorti. We got the hell out of there. Don't know what was going on, but everyone else was in hurry to leave and we just followed - quickly. And never looked back.
The other time was more recently in Turkey, on a private tour in a small van with six people, tour guide, and driver. We were on rural road with we ran into a road block. It was unexpected and the tour guide seem a little concerned and surprised. The tour guide spoke with one of the officers, came back to the van, and announced that we should exit as they wanted to see our passports. We exited, handed them our passport one by one, they checked the passport and the required visa stamp for Turkey and we left. Later the tour guide said it was just a random road block.
Just remember a third time a couple of years ago. We were on the DBahn bus to Prague from Nuremberg. We were still in Germany when a squad car with flashing lights directed the bus into a rest area off of the express way. A second van with more police officers followed the bus off the road. It was announced that this was a routine passport check. Two officers came on the lower level checking the first class passengers and a couple went upstairs for the second class. They removed an individual from the upper level and we left after about 20 minutes delay.
The point is - it is possible to be checked. Maybe your driver license or color copy of your passport will work for you but I like having my passport handy.