Any reason to SIR sooner rather than later?

Unless it gets you a better spot for housing which seems unusual, why not wait until the end? I’ve talked to some of the UC Eng schools who say they give scholarships through the whole month of April, I would have to believe they would not bother to give a scholarship to someone who has already committed. I would think if their yield is lower than expected, they may give scholarships towards the end of April to boost their yield. Is this crazy thinking?