Every book that I've read about veg. stipulates growing brassica seeds
either in trays or a seed bed and later transplanting.

I know that germination rates can be iffy, and that doing things this
way means that you can transplant the healthiest plants, but are there
any other reasons for *not* direct sowing?

Why would it be such a bad idea to plant (say) four seeds at each
station in the destination bed in the first place, and later thin out
in-situ?

Any feedback welcome - nobody I've asked knows why this would be a bad
idea, just that they've always done it differently...

Thanks,
Patrick