Hi, 

I had a benign tumour removed from my tibia, just below my knee in 2018. It was biopsied initially and then investigated again when it was removed at the surgery. 

I think they do it just to triple check that the entire thing is totally fine and there was no little pocket of abnormal cells inside it that they might have missed. Obviously if there was, it's been removed anyway but I think they do it just to make extra sure. 

That's how I understood it when I had it anyway! 

They did that for mine as well, because the doctors were unsure what exactly the lump was. Second time came out benign as well. They're just making sure. <3