For an invention patent, there must be a specification that clearly and completely explains the technical scheme and the scope of the technical scheme that the claim clearly requests protection. Even if there is only one idea, if those skilled in the art can clearly know what the technical scheme is from the description, there is no need for drawings.
For the patent of utility model, it must be an improvement of the shape and structure of the product, so there must be attached drawings.
Design patents should also have pictures, which are used to determine the scope of protection.