I have heard that you should do this, but i don't honestly think it would make much difference in the long run.

i do plant my cucumbers and melons on there side,they have less chance of rotting

as seeds land in all positions they could well fall on their sides. They will grow correctly roots down shoots up.

I always sow "flat" seeds, such as courgette, sunflower, pepper, etc "vertically", as read years ago that this improves the chances of germination. Have thought, sometiimes, of trying sowing both vertical, flat and random sowing as a comparison "study", but that will have been done, somewhere, and I dom't have time, lol!

Having. obviously, deduced, that, by sticking them in vertically, pointed end down, you can sow more seed in a given area than you could by laying flat, but,. interesting to note that. by doing so, I always get the number of shoots from the seed I sow, eg. 4 rows of 3, or suchlike.