Advancers are only installed in efi cars and alto and other carby cars dont come with it. Carby cars running on cng are advanced manually on petrol settings so that when u run it on petrol, engine will knock but perofrmance on cng will be enhanced, both in terms of economy and acceleration.
As far as my knowledge goes, there is no harm in advancing your car for the sake of better performance on cng, at least in the short-run. In fact you'll find that all well reputed cng mechanics follow this practice.