Schools differ in policy for different reasons.
Possible disadvantages of study leave;
The ones that need the most help won't be doing any work at all.
The students with SEND would benefit more from targeted intensive support to help them do their best and not panic/freeze/refuse/forget how to operate reading pens and other assistive devices.
Some who always struggled with transitions might be unable to go back for exams.
The most vulnerable aren't in a safe environment.
The most vulnerable aren't necessarily getting fed.
Some might not see a single teenager/talk to anybody for weeks because of various factors (eg, parents who won't allow it, anxiety, caring responsibilities, expectation to work, lack of online facilities).
Kids vote with their feet and don't turn up for exams or arrive late.
Rampaging teenagers in town centres.
Rampaging Y11s across the school site.
Lack of staff to supervise due to the ongoing shortages and budgetary constraints, meaning that it would require taking experienced staff away from the younger year groups to maintain control, leaving the 7s-10s with expensive supply/cover supervisors.
The period from now until the last Friday in June is still compulsory school age.
Coding S is an authorised absence, so causes the official attendance figures to drop significantly. Y11 attendance data isn't taken into account in the second half term, but 3+ weeks of study leave before that point makes a significant dent.
Ordinarily compliant students can go a bit demob happy and suddenly start doing absolutely ridiculous things because they see it as they've left school and can be absolute bloody idiots both outside the gates and when back for examinations.
Possible advantages of study leave;
Kids who can work at home will.
Not having to wrangle the aforementioned rampaging Y11s.
Being able to start putting the most experienced teachers with lower years.
Having staffing capacity to come down hard on Y9 who are very aware that they're not doing X subjects in September and will make sure that everybody knows it.
Being able to do more intensive/interesting/fun things with lower year groups.
Capacity for trips and events supervision.
Staffing for Sports Day.
Capacity to potentially start Y9s on the KS4 curriculum early.
Depending upon the particular cohort and policies, local picture, etc, YMMV with either approach.