I've always balanced them. No screws now on my 9" slicks. I don't remember if I always screwed my bracket Challenger 14x32's years ago.

I have a theory that the unbalanced, bigger, low pressure tires will not be felt as much as unbalanced, smaller, high pressure tires. I run my 9" slicks at 21 lbs. That also lessens the need for screws. I sometimes mark them and do see that they move a bit even at that pressure. They move back somewhat after I swap them side-to-side and eventually stabilize. It does bother me not to rebalance once or twice through the tire's life. But it's usually too inconvenient to do.

Another theory of mine is that just because you don't feel it, it doesn't mean it's not there. It's splitting hairs, but if an unbalance is trying to move a tire up & down, even a bit, while going down the track, it's wasting energy that should be accelerating the vehicle forward.

At some point, enough added weight may offset any benefits of a balanced tire. But I've seen some tire/ wheel combos balance better by just rotating the tire on the rim during mounting. Nothing is "perfect".