Laser hair removal and shaving
Shaving does not cause more hair growth with laser treatment (or any other time). I require my patients to shave prior to their laser hair removal to decrease the risk of burn and pigmentation as cited in another answer in this thread.
You do need to avoid the sun when having laser hair removal. You can safely shave the hair in between the laser treatments and just before treatment.
Laser Hair Removal and Shaving
For laser hair removal to be effective, hair needs to be intact in the follicle, but should be short and shaved for two reasons: First because if the hair is long, the long portion of the hair will absorb some of the laser's energy as opposed to all the energy being directed to the hair bulb itself, making the treatment less effective. Second, since some of the laser's energy will be directed to the hair laying on top of your skin, you risk receiving burns and unwanted pigmentation. In our office, we would not require you to shave your legs because we will shave them prior to treatment so that all of the energy can be focused on the bulb, the growth center of the hair so that the treatment is maximally effective.