As we discussed back in Week 1, the term "situation" refers to the surrounding context that impacts a player's expected performance in a given week. It's a broad term because there are so many factors that go into it.
But when a quarterback switch occurs, everybody's situation changes drastically. And we've got a whole bunch of them in Week 3.
On the main slate alone, there will likely be six quarterbacks starting for their respective teams who did not start in Week 2. This means we've got to re-examine the situation around each and determine what impact it has on the fantasy value of the pieces around them and whether the quarterbacks themselves are in play.