Transplants have a place.

This year transplants saved my garden, more than once.  I prefer to plan seeds when ever possible.  There's more variety, and the plants seem to grow so much better.  Sometimes life happens, and it's just not possible, or practical.  The winter of 2020 I took my fence down around my garden to redo a raised bed and add a new one.  Unfortunately the garden project kept getting moved to the back of the Todo list.  The chickens ate, and or destroyed everything in the garden until the fence was replaced. It was May before I was able to plan anything. For my area this is super late.  Thank goodness I was able to buy veggies already started.  Maybe about a month? later Mr gopher showed up and took out a bunch of veggies.  Back to the store.  I wouldn't have had any produce, this year if it wasn't for transplants.
I have never grown broccoli before.  I bought two plants about 3 weeks ago. It is growing beautifully.  I'm so thankful I did because I also planted seeds. I don't follow seed spacing anymore, I've discovered I can grow so much more in less space.  But I didn't know how big a broccoli plant gets.  Thanks to the transplant I will thin my broccoli so it will have enough space to produce.
So although I still think planting seeds is best, I'm grateful there are plants I can buy if needs be.

I've consistently found that transplanting butternut squash and cantaloupe gives me twice the harvest in my short season.

Transplants surely have their place.

I’m working on a new community food farm project, and because of the wind, about half the varieties we direct seeded perished. So we next tried growing our own transplants, and that worked far better.

As Mike says in a short season, plants that have been started in warmth undercover are sometimes the only way of getting a crop I suspect that this will more efficient that lots of separate little propagation stations in individual greenhouses/windowsills.
I was so busy this spring the moment for sowing my tomatoes came and went, luckily I was gifted plants (which were surplus to their requirements) I got a really good crop and one of them is a lovely fleshy plum which I can save the seed from and try again mysefl! Sharing surplus plants is easier for me than culling the seedlings!
The other advantage I can see is that if you only have room/need for a few plants then you only need to get the few that you need, rather than having that surplus to deal with.
Having said that I don't think I've had transplants for hardier veg. I find the slugs go for brassica and french marigold transplants in preference to anything else! Soft grown plants tend to need looking after rather more than my neglected pots!

Of course they have a place! I think the most beneficial thing about using transplants is that you can keep the soil covered for longer (since direct seeding usually involves a lot of disturbance, which is very damaging to your microbial populations, introduces a flush of weed seeds, and leaves your soil prone to erosion). You can also spend less time "weeding," as if you've kept on top of the weeds your desired crops will have a good headstart.

I grew the best leeks this year ever.. I bought the plants 1600 organic leek starts from Holland, set in in May produced leeks in September. Leeks are one of those things that has to be started under lights in January if you want them before winter.
I start all large slow growing plants like broccoli inside and plant them out, they take up the bed for long enough as it is so the 3 weeks they spend inside helps. Onions also have to be started in Feb under lights if you grow from seed here (which is why sets are more traditional)

In my garden, I often lose brassicas and lettuce at the seedling stage.  This year I got some napa cabbage, spinach, and stem lettuce starts at a spring plant exchange and they grew beautifully.  Much better than any of my direct seeding attempts.  

And of course leeks, as Skandi said. (though I started those myself). And tomatoes, because we can't get ripe tomatoes unless they start indoors.

I can second (or third... or fourth, or whatever :) ) the need for those of us in a short season growing. Here in Maine, if you don't start seedlings or buy seedlings there are a lot of plants you won't get because there is not enough time to grow them apart from greenhouse or some sort of season extender.