This is somewhat true when flowering seed grown plants--but only when pruning growth tips or pruning from the top-down....however when pruning from the bottom-up, often done when "tree-forming" ornamentals as recommended--the plant will rarely feel this let alone show much impact......
This will encourage upper cola formation by completely eliminating flowers on the lower third of the plant while maintaing enough airflow to allow you to grow plants at 4x the density without the worry of molds and fungi attacking the dense foliage and adjacent flowers.
I would also like to note that the more you prune growth tips (as we all know) the more division occurs and thus creates an open, vase-shaped bush......
if flowering from seedlings in a tub where space between plants is the issue--or less so than height--DO NOT TOP--Prior to flower.
This will leave only a single leader plant that will grow tall and narrow if crowded--regardless of species (indica or sativa--this forced stretch occurs because the plant measures the amount of available light in the red spectrum and when crowded most red light has been absorbed from the neighboring plants so they stretch in an effort to reach more of the desired spectrum.
This will be the closest thing to a lollipoped clone you will be able to grow from seed and then pruning--from the bottom-up as recommended can be done with no ill effect. And alot less manicuring by eliminating the fluffy popcorn you would otherwise harvest from the lowest branches.
If he flowers in a 24 gallon rubbermaid with the net pots 2.5 inches apart and the last time he prunes is 2-4 weeks before flower (implying 2-4 wk veg time after last prune+veg time prior to pruning) he will end up running out of room and will be forced to sacrafice a plant or three.
Your seedling won't act quite the same as my clones but this is what you want in an ideal world where net-cups are installed 2.5" apart by the manufacturer
7 days into flower--first pruning, bottom-up
18 days into flower--second/last pruning
Then you only need a half inch between pots..........

-OitW