Propane forges are clean. There's no smoke. No smell or no spark is flying out to set your shop on fire. They get plenty hot to forge. Well, they're pretty easy to control. And, they're pretty simple. Moreover, propane gas forges are simple to operate. Therefore, they're not too expensive. You will get readily available fuel. Really, just a laydown that they're the most complete solution to a forge for most modern makers.  But yes, there are some advantages to charcoal and coal, but for most knife makers, propane forges are the best solution.