Once you let the kid into your classroom:
A) they are under your supervision. If you were planning a quick dash to the loo or the photocopier, now you can't unless you escort them out first - & no, that doesn't mean hanging around the corridor unsupervised.
B) you can't make confidential phone calls, join zoom meetings or - if a KS3 student - cue up a 15 certificate video clip for your GCSE class in two periods time.
C) you will get a bollocking from SLT for breaking the 'no kids in classrooms at break', which is a blanket ban in most schools, so they don't blow themselves up in a lab, or nail themselves to the wall in a workshop.
D) you are putting yourself in a seriously dicey safeguarding situation, as you are now alone with a child in a scenario where you are both breaking scho rules.
So yeah, if the kid is a repeat offender it needs investigating to see why, but a sanction may very well be apt here.