In article , Martin Sykes
writes
If a hardy annual or biennial doesn't die off naturally after flowering then
is there any good reason why I should dig it up instead of leaving it in
place to flower next year?

If it's an annual in the botanical sense (rather than the gardening
sense) it will die after setting seed anyway.

If it's an annual in the gardening sense, which includes perennials that
don't make it through the winter, then there's no reason why you should
dig it up other than the aesthetic one that sometimes plants get a bit
leggy and untidy in their second season.
--
Kay Easton

Edward's earthworm page:
http://www.scarboro.demon.co.uk/garden/