Probably a little of both insurance and higher sales. I always plant double and sometimes triple the seeds to insure I get enough plants. My problem is I have a hard time just clipping those extra plants and end up with way too many. It's not hard to find homes for the extras though once my gardens are full.

I do not waste seeds like that. Some are too expensive to just pinch back 1/3 of what germinates. Besides even if it isn't that expensive it's a waste

When sowing in my greenhouse I start my seeds in shallow containers. You could do the same using lights. My favorite is the 4 x 41/2 x 2 inch plastic containers that mushrooms come in. I put drainage holes in the bottom. When my seedlings get their second leaves--or sometimes before that--I transplant them into individual containers.

When direct sowing I thin and transplant too. In the garden when sowing small seeds like carrots it is easy to get them too thick. I will thin them and cook up the little carrots. When they are small like that and fresh from the garden using a scrubbie removes the skin.

So don't waste seed. It is not necessary

I have had the same thought. And like Taz, I can't bring myself to pinch off or thin out seedlings.

I think the whole idea behind square foot gardening where you plant one seed exactly the spacing you want it is fantastic. If something doesn't come up then put one more seed in that spot.

Check out the square foot gardening forum. Lots of info there.