Most bowlers feel that lane courtesy is very important. You can see it all the time, especially in open bowling where one person understands lane courtesy and kind of looks down on the people next to them that may not know.
Lane courtesy is simply the act of letting people next to you bowl without worrying about you being on the lanes at the same time. Usually lane courtesy only applies to the one lane to the immediate left and right of you. If there is someone bowling on those lanes, just sit back and wait your turn.
The PBA follows a different style. The make you wait for one full pair of lanes, so you will have 5 lanes of uninterrupted bowling. When done properly, this method actually increases the pace of bowling.