This question is often being asked by Operation people. From designers’ point of view, the equipment is designed with the draft and the pressure of the furnace or the reformer. From that point, the draft available is determined to size the burners, and size Induced Draft and Forced Draft fans. If everything is designed correctly, you should not need to change your draft at all. However, over the time, the furnace may be running old or burners may not be operated or designed correctly and may need to adjust the draft.
As a conclusion, unless there is a very good reason to increase the draft, normally the design draft for furnaces or reformers should work. However, if we have to increase it due to flame stability, first thing to do is to have the burners checked to ensure that they were designed, tested or operated properly.