I agree to both ways. It just depends on each persons situation. With chicks, I think you will need the heat for them just like you would if raising them in a brooder until they are old enough.
My coop is a 8 X 12 shed 9 ft. high.I have 9 in my flock + 1 resuce without most of her feathers. I do heat with a 250 watt bulb in the 20 degrees and below. my coop never gets below freezing. It comes on at about 6AM and goes off about 6AM. If it is subzero out and the coop gets cold during the day, i have the lights on a timer, so I can periodically turn it on and off. I usually use the red heat bulb in the night and the white bulb during the day if needed. I have not noticed the red light making any behavioral or egg laying changes as well. My coop does not get above 55 in the winter. I know, I know they dont need it, but they are fine (going on 3) but it makes me sleep better at night knowing they are cozy. They have free choice to go out from sun up to sun down. Sometimes they do, sometimes they dont. I have one with some missing feathers, and she stays in when its cold, and goes out when the sun shines or warms up.
My rescue with 80% feather loss has the heat lamp available to her as well right now until she feathers out. This is the lamp that sheds it extra heat to the coop.
Spoiled spoiled I know.... They are all healthy as well, I have not had any heat related issues from them.
I do think if I had another 5 or 6 girls in there I probably wouldn't need the heat. They would produce enough themselves. Oh oh OHHH!!!! I see a need for more girls!!!!