Usually in a game of Carcassonne, you will have most of your meeples constantly in action, reserving one or two "just in case". Since the turn order of the game has you placing a tile, then placing a meeple, then scoring, then removing scoring meeples, you can score what we like to call "Cheap points" if you get tiles that are not really helping you otherwise.
In this example picture, I placed down a straight road tile that finished the road between the city and the cloister that my monk is on. Because I had a Meeple left (the Big Meeple, in this case), I get to score "a cheap 4 points" for finishing the road.
When we play, we automatically assume that if you play a tile that completes a road or city that is unoccupied, and you have an extra meeple that you don't want to play, you automatically get the cheap points. Many a game has been won or lost by as little as 2 points.
