More flexibility and light control. Positioning is needed other than rotation.
Thanks for the suggestion, can you add some more details on what specific controls you’d want and why. When you say sIBL layers, which layers are you looking for? What do you want to do with them? Do you want to solve this through sIBLs or do you want additional individual lights?
I use an application for 3D where placing an sIBL into an environment gives you 3 layers--lighting, background and reflection and control over location, layers (blend modes, etc), etc.
It's a very quick way to do a lighting setup--I usually use the lighting and reflection and turn off the background. Being able to control location, colorspace, and visibilty gives a lot of control over the lighting and you can add individuals lights as needed. Some of the sIBL come with backplates to use for compositing which is helpful if you want a background based on the lighting.