So in the USA a big pool of people get called. You tend to sit around a while, waiting for a case. If you get called for jury selection, if you get excused for reasons like those in this article, you tend to get to go home. If they’ve filled a jury before getting to you, they tend to put you back in the waiting room, to see if they can use you for a different one. If by the end of the day you haven’t served, you don’t have to come back until the next time you get called.
Now, this is Baltimore. But my sense is it’s a pretty similar process in other parts of the USA, at least in other cities.