There's a lot of misinformation about SATs, especially on here. With the changes made in education over the last 10 years, the SATs have become increasingly important/impactful to the child.
The main reason is one that many parents and even many teachers are unaware of. A core measure when judging secondary school effectiveness is their Progress 8 score. This measures how well they develop children from their starting points as measured in their SATs. Secondary's own tests are irrelevant for this. A 0 score means that children make the expected level of progress, a negative one shows lower than average progress and a positive one shows higher than average progress.
Senior leaders are constantly monitoring the rates of progress both at a cohort level and at an individual level. They then have this in mind when making decisions about the school, ranging from how to set children to where to deploy their most effective staff to which children get access to additional support/challenge/intervention.
Children having a higher target, due to getting higher SATs scores, means that they will be challenged more and, if they go off track, they will be brought back on track through support and intervention.
Children having a lower target means that less will be expected from them and, in some cases, if they are already on track to achieve that lower target, they won't be prioritised for support/challenge/etc.
This is not necessarily how education should be but it is what is happening practically in schools at the senior levels of leadership.