I'm new to all this, but here's my take....
if the frame is too small, you have to raise the seat a lot. By doing that, you sit hunchbacked so as to get to the handlebars which are then very low ....
ride 50 miles in that position, and your neck takes strain as you have to lift your head up high to see where you are going
I have ridden a few bikes, and prefer a slightly bigger frame that what the calculators work out for me (as long as both of my feet touch the ground when I'm stopped at a traffic light, I'm happy) .... I'm much more comfortable on these larger frames even though the seatpost is a lot lower down than what most riders set there's to
Agree 100%. Back when I used to ride my old hybrid, it was a size medium, or 18". I am 5'8", used to be 5'9". The bike was sized correctly for me at the time but the bars were so high I sat too upright. So I switched bars to a lower one, which left me hunched over. On rides over one hour, my neck would start to hurt from being too hunched over.
My current bike is a much larger frame, 55 cm, with drop bars which stretch me out much more. And the larger frame puts the bars at the right height without having to mess around with spacers.
No more neck problems.
Better to be a little stretched out than to ride hunched over. Other things being equal, go with the larger size.