well in other 3D software they are fast. and if you are going for artistic lighting you need 100% control. why do you think Pixar is not using 100% GI? because they can not control it. GI is physical correct and you can not control it.

and for fill lights using always raytraced shadows is very hard . thats why i think if the DM shadows work good then we can use them for fill lights and for some extra color or even for Rim lights. but not for sun or for realistic shadows.