Return on your seeds

When I buy packets of courgettes, peppers and even tomatoes, there tends to be just a few seeds while with carrots and brassicas, you get hundreds and often for a cheaper price. A lot then depends how you grow them. Beetroot for example, I grow 2 to 4 together about 4 inches between clumps. Then pick the biggest and let the rest carry on growing. So I can carry on picking beetroot till late autumn from about 2 weeks ago. With carrots, a 10' row should produce about 10lb of carrots - which should use only a fraction of a packet of seeds. I tend to space about 1" apart in the polytummel and hope carrot flies don't find them which they tend not to. Again a double 12' row lasts quite a long time bit not as early as beetroots.
Carrots you can leave to carry on growing until you want it, the longer you leave it the bigger it gets - and still tastes like carrot while courgettes will carry on growing if you leave them but they morph into marrows and the plant stops producing.