The main reason to take the flowers off is because they take energy away from the foliage production. If you tip prune to remove the flowers then a bit of that new growth comes off too.
I’m letting mine heavily flower this year (this is its 3rd bloom this year by the way) because of the hummingbirds, bees and butterflies. They love feeding on the blooms.
Coleus are great in containers and combine beautifully with other plants as you can see here from my melange.
Whether I remove the flowers on mine or not, it seems to get the same size and grow into the same crazy form.