Belonging to a country where incense sticks are used extensively, I wonder how bad are they, althought it is said they are good for air. But at moment, it seems highly misleading to me. What are the health issues related to regular inhaling of the produced smoke?
This question has a different answer depending if you are indicating consequences on air quality or on global carbon cycle (i.e. climate change), and I would say it is similar to asking the consequences of lighting a cigarette.
About air quality: the effect is similar to the one made by every kind of wood combustion: air with some smoke that sure is at least a little less healty than air without smoke (release of CO2).
About carbon cycle changes: there is no consequence if the wood did not come from a plantation up exclusively to generate wood to be cut. This is because the wood that is cut and burned relases the same compounds (mostly CO2) that it would release if the tree it is coming from dies naturally and its parts naturally biodegrades.
Please note that in this second case the problem does not come with the fact of burning wood, but with the fact that the wood to be burned comes form a plantation and it is not collected by the naturally dead trees or fallen branches.