I would love to say that SATs don't matter in secondary school, but my experience is that unfortunately they do.
My dd didn't get her SATs results (whole year group annulled, not the children's fault) and it's been a complete PITA for the whole of secondary school. Yes, they set according to CAT tests, but my dd's targets were based on her getting the lowest possible SAT score so basically failing. Despite my asking several times that her targets be adjusted, they weren't, so dd went through KS3 with every teacher expecting very little of her. Despite her doing well and knowing that the low expectations were because of her non-existent SATs results, this really affected her confidence and self-esteem.
At the beginning of Y10, the school looked at the data, decided which students needed to 'show progress' and moved my dd to lower sets. She was doing work that she'd done in primary school. They wouldn't move her up, basically because it made no difference to their data how she did.
I moved her to another school (not just because of this although actually learning something is what children go to school for) and she was put in low sets as the data from her previous school showed her targets to be very low. She quickly worked her way up, but missed out on vital parts of the curriculum with set-hopping. We're lucky enough to have been able to afford some tutoring in subjects where she missed enormous chunks, and she's pretty much caught up now.
The lack of SATs results meant that her predicted GCSE grades were lower than she scored in her mocks (computer algorithm put a ceiling on what she could be predicted). Although these were adjusted, it wasn't in time for her to miss out on a sixth form offer that she wanted.
I cannot wait for her to finish KS4 and never have to think about bloody SATs again.
Her younger sister didn't do SATs (one of the covid years). Schools seem to have coped with whole year groups with just teacher assessment from primary school, and it's a crying shame that they couldn't have abolished the SATs altogether.