La Puce wrote:
[...]
and peas (frozen) and leeks. But my spuds went in as seeds in March
(easter day is the custom). I had potatoes in June, these where my
earlies. Why would one do it in September?
[...]

It's a perfectly normal thing to do: I'm amazed you haven't heard of
it. You do it for the delight of having fresh home-grown new potatoes
at Christmas.

Having said that, I'll admit I've never done it myself.

Another thing people do is to plant early varieties _late_ : that can
extend your cropping. (They are early more in the sense of being
quicker than of needing the conditions found earlier in the year.)