A greenhouse is a structure made mostly out of glass and metal that is used for raising plants in a protected environment. A conservatory is an extension of a house or building that incorporates a lot of glass.
Sunlight is essential for pretty much all plants, and this includes cannabis. Because a lot of glass has been used in the construction, the sun will illuminate the plants and by doing so serve as a free source of energy. This is advantageous for growers with a limited budget, as lamps do not need to be provided.
The biggest benefit of a greenhouse or conservatory is the protected environment in which the plants grow. Because the plants are not stood growing unprotected in the outdoors, it is easier to keep them free of undesirable bugs and diseases. In addition, it is also possible to control and adjust the atmosphere in the space. This includes the air moisture, ventilation, CO2 levels and so on.
One possible drawback to using a greenhouse or conservatory, just as with all other growing techniques that rely on the sun as the source of energy, is the loss of control over the lighting. This allows the plants to run through their natural cycle to and pop into bloom as soon as the days star to become shorter (in the autumn). For this reason it is a good idea to prepare the plants in spring for growth, so that they can enjoy their full lifecycle before they have to be harvested.