Pinching is a third technique - In the short pinching is a stress technique, and stressing a plant is thought to produce more resin. Like cropping or topping you promote the plant to grow out more then up. The plant gets bushier. Pinching will diminish the overall yield but not really the overall weight.
so its bad to pinch?

i herd if you pinch it, another one grows... so you get 2
now i hear if u top it.. another one grows with it.. so you get 2

but if you top it, ur cuttin the piece off so how does that get you 2 if u cut one off?

and if how do you get 2 if you pinch it, which should "diminish the overall yield" ?