UK - What difference would having a "paying guest" lodging in your house make to your home insurance?

I am currently in the process of buying my first house, and had thought about potentially letting out the spare room to a lodger some time in the future.

Having just paid for a home insurance policy, I was asked during the application process about any lodgers who might also be living in the property. I won’t have any when I first move in, so didn’t need to go through this at that point… however, if I were to have someone lodge with me in the future, what are the reasons I would need to "update" my home insurance policy? Is it just because the number of people living at the property will have increased? The contents will obviously increase too, given that they would be bringing possessions with them- so would it just be a case of updating the insurance policy to cover that new, higher value, or is there more to it than that?