Were you veging or in flower when you cut the leaves and for how long? Are you growing in dirt or hydro? What are you lights? etc.
I'm fairly sure that you've learned this lesson already, but just in case...
Research things before you do them, especially if it's something incredibly drastic like cutting healthy leaves off of your plant. Does your mate have lots of growing experience? Question every piece of advice you get. Who does it come from? What do grow books say? Also, you can try to do something as an experiment to one of you plants, don't do it to all of your plants.
What's done is done. I don't think that there is much that you are going to be able to do except play with how long you keep the plant in veg, if that's where you are at. If you still are, you can keep it in vegetative longer. Your plants will most likely still grow and do fine, you probably wont' get as much bud.