I'm a bit late to jump on to this, but here goes. There's a subtle difference between 0.5 and a half. A half is exact, it's one divided by two. Unless you're talking purely about numbers, it's usually one of something divided by two. So the question is, what's the something?
If you're talking about a million pounds in normal conversation, it's vanishingly unlikely that you mean exactly a million, no more or less. It's much more likely that you're taking the million as your focus. By contrast if you said 'a million, two hundred and ten thousand, one hundred and three pounds' then a single pound is your focus. Adding 'and a half' means another half million in the first case and another half pound in the second.
This is reminding me of significant figures. There's no difference in value between 1,000,000 and 1,000,000.0 but they carry different information and therefore have subtly different meanings.
1,000,000 - at least one significant figure but I can't tell for sure how many.
1,000,000.0 - eight significant figures because the final zero after the decimal point doesn't have to be there, its only purpose is to say that there are definitely no tenths. The intermediate zeros now give real information instead of being just place holders so they become significant too.
Pedantry and number theory together, all my Christmases have come at once 😁.