Not only seedlings should be treated this way. Any plant, regardless of propagation method, should be allowed to get just a hair rootbound, then allowed to dry out a bit, before gently upending the pot while supporting the soil and stem with a flat hand, rapping it on the bottom, and letting the intact rootball slide out.

Shown is what your root ball should look like when you transplant.
The next pic is a bunch of clones that have just been potted into 2.5" peat pots and can be carried around in a tray and stuck wherever there's a 1x2 foot bright spot in the grow room. I do the hardening-off during this period; the ones with domes are a week 'younger' than the ones without.
Next, is those same clones given a week or so of veg time to establish a healthy root system and stuck under a HPS1000 to grow on and flower- I don't want to re-pot them until they NEED it, so they are still in those little pots! lol
Finally, 2 pics of a flower room that shows new arrivals, month-flowering plants, and a few large retired moms in the back corners blocking off those dark edges of the room.