I believe you want to do it if your buds are airy and long/ you want to stop some from reaching the light and encourage the lower growth to catch up and even out the canopy is what some are saying but then MOTR says she gets 10-15 % more buds so…
https://overgrow.com/t/backfilling-buds-by-trimming-the-tips/18859
Edit note: the link did not update and shows a pre-edited version of the dialog