Other medical marijuana evaluation clinics offer pieces of paper known as "Grower Permits" "Grower Licenses", and "California Exemptions". The claim behind these pieces of paper is that a medical cannabis patient can legally grow more than is permitted under S.B. 420.
The value of this piece of paper? 0.07 cents.
The cost to you? $125-$200 plus the cost of your evaluation. If you have to present the piece of paper in court? The cost could be as high as a prison sentence plus legal fees. Such "permits/excemptions" actually offer less protection than the consitutional rights you already have under California State Law and Proposition 215/S.B. 420.
From California NORML Patient’s Guide:
HOW MUCH CAN I POSSESS OR GROW?
Under Prop. 215, patients are entitled to whatever amount of marijuana is
necessary for their personal medical use. However, patients are likely to be
arrested if they exceed the SB 420 guidelines. SB420 sets a baseline statewide
guideline of 6 mature or 12 immature plants, and 1/2 pound (8 oz.) processed
cannabis per patient. Individual cities and counties are allowed to enact
higher, but not lower, limits than the state standard. See local limits.
Patients can be exempted from the limits if their physician specifically states
that they need more. *
*In a state supreme court ruling, People v. Kelly (2010), the court held that patients can NOT be prosecuted simply for exceeding the SB 420 limits; however, they can be arrested and forced to defend themselves as having had an amount consistent with their personal medical needs.
More information on Growing Guidelines can be found here:
California NORML's List of Local Cultivation/Possession Regualtions by County and CIty
California NORML's Tips for Growers and Collectives
California Attorney General's Guidelines on Growing Medical Cannabis