Often flights will leave the cruising altitude long before the actual landing. They will go down to a couple of thousand feet and stay at that altitude and circle for quite a while in waiting loops before it's actually their turn to land. It can be seen basically all the time at Heathrow Airport (LHR). But also for example in Munich Airport (MUC), where flights often come far down over the city and then make wide turns towards the airport.
So I'm wondering: if it's already clear ahead of time (and I'm sure mostly it is) that it's not their time to land yet, why not circle at higher altitudes? Often those waiting loops occur over dense populations and thus create quite some noise on the ground.