The smoke diffuses and attenuates the light which is to the benefit of the plants. By diffusing the light, the light seems to come from more directions, so the shadows under the top leaves of plants are less intense and the lower leaves are more effective at producing food for the plant. Normally, the shaded leaves become more consumer than producer of food. By attenuating the light, the intensity of the direct sunlight is reduced and the incidence of burning is reduced a little. There are concerns about greenhouse gases.
Carbon dioxide is actually a benefit to the plants.
A plant uses carbon dioxide to make sugar and other foods for itself and us. Any increased carbon dioxide levels around the plants would be carbon dioxide fertilization for the plants. So, there may be little carbon dioxide fertilization effect. I can't address what is happening in the upper atmosphere and the effects of carbon dioxide at that level. To summarize - the smoke, by altering light intensity and any potential carbon dioxide increase, may be beneficial to our gardens.