It really depends on what you're growing and how. If these are photoperiod plants in veg, topping twice is enough unless you are manifolding them. For scrog, once or twice is plenty. Forcing the tops into horizontal growth leads to more cola sites faster because every growth node along the way will make bud. There is always a bit of a recovery period after topping so know that every time you do it, veg will take a bit longer. For autos, I have no experience but some of the folks on here have done it. Some recommend it and others say it isn't worth it because veg time is too precious.