Not sure

I have just started growing and have spent pretty good money on good genetics. I have about 12 plants at about 15 inches tall. A friend of mine has been growing for about 30 years and topped my plants for cloning and told me this would help the plant as well by making them grow thicker he took alot of tops about 45 of them and told me to give it about three weeks and then go from veg to flower. My question is did he just want my genetics or was he right. I have a 4X8 room with 6 400 watt LED.