What happens if you transplant without hardening off?

Is there anyone out there who does not harden off their seedlings? Do they survive? Are they stunted? Or, do they all die?

Just curious.

It depends on how extreme the difference is between where they came from and where they are going. I keep our house at 78 degrees (A/C year round here, pretty much). When the weather outside is within a few degrees of that I have transplanted without hardening off. I've also transplanted in hotter weather after only a couple of days of "hardening off" by putting them on our shady porch and just leaving them there. They've done fine.

Changes in temperature and light levels can be stressful for plants besides just the stress that can come with transplanting. If you don't harden them off they could die or it could slow their growth.
So, although I know it is recommended I rarely harden off my plants. I do try to transplant on a day when the light levels and temperatures will be less stressful. I also usually start my seeds in either compressed peat pots on my Aerogarden which reduces the stress caused by transplanting because there is less damage to the roots. I also sometimes cover the transplants once they are in the ground - either to shade them or to protect them from colder temperatures.

Hardening off allows the plant to develop a stronger outer layer on the leaves. The waxy layer protects them from UV light and from drying out. Without it, they get wind/sun burn. Since transplanting is already stressful, the combination of transplant stress on top of getting burned/dehydrated *can* kill them -- but my limited experience is that they usually survive.

Below isn't a great comparison for this thread, because there's additionally time/environment variables ...but it's a good enough fit: The lettuce on the left was started inside, the one on the right, outside --BUT the outside lettuce was started 3 weeks sooner.
I had to leave for several days and due to some poor planning, my choices were to transplant the indoor lettuce seedlings without hardening them off or let them wilt to death inside. This is what I came back to about a week after transplanting:


The white areas on the left lettuce are burns, either from the sun or wind, or both.
The lettuce looks better now that another 2 weeks have passed:

but it will probably always be a little behind where it could have been had it been hardened off.
(The holes are probably from sowbugs. They're being a real nuisance this spring.)

It's less of a thing with lettuces but hardening off also allows seedlings the impetus and time to develop a stronger stem. The stronger stem keeps the tender stem from snapping in the wind. This part can be accomplished indoors with an oscillating fan (not from the start though, because the fan will dry out the surface of the soil and inhibit germination.)