Light precision work ok on impact and other bags, a Heavy Bag should be Just That Heavy and Hard base...And all bags should be trained static and than placed in linear or circular motion...my opinion follows...
1.) The double end speed bag work followed my makawari work, I know from experience that
a.) if used inflated well and taut enough, practice required bob-n-weave as well as training to not shoot both hands out, If struck within proper closer (toe near bottom cord attachment) distance with power...that bag can hit back quite well (My nose and face know as it decreases time to react to recoil) if a hand or shoulder/arm was not ready for recoil. Great for fine motor skills and trial and error of combination as well as training rapid repeat kicking drills.
2.) Using a Hanging heavy bag (not one of those goofy water bags resting on floor)...was power training and as it was hanging, if a power Impact was applied the Heavy bag would respond differently than to a push ( I practiced both). A strike that is a push causes the bag to swing, a power impact either stops motion or creates a rocking motion and settles to center and also displays a "folding" at point of impact (The heavy bag I used was 100 lbs and the sawdust had settled in gradients to bottom so low leg kicks and low hooks or upper cuts were last as more body conditioning)
3.) as with both bags many people approach the bag as it sits static...more realism can be had by setting either type of bag into linear or circular motion prior to attack, causing one to use footwork to achieve closing or retreating attacks
a.)a Hard bottom heavy Heavy weight bag is great to condition shins and forearms while moving and (ergo makawari work prior) ensure that punching/chopping/wrist and palm power impacts have proper wrist and striking area of attack locked to avoid the bag broken wrist (recommended advanced only, start slow cause that lower heavy bag is a sawdust rock). Light heavy bags will not have the bottom weight to display overtly a push from a shocking impact and are for the unfamiliar to avoid injury. The well used Heavy bag if set in motion can bite back too...
***the motion of a weighty Heavy Bag can distinguish push from shocking impact. Practice of Pushing to uproot is also a good drill...Does the opponent stand still??? Neither should the Bags. Impact pads train more adaptability to change if the holder is good and safe.
Just my humble input.