It depends on your sub base.
If you have coir/verm you get all the tiny valleys and bumps that are ideal for fruiting, so a casing layer doesn't add much benefit if your humidity is good. For pinning, there are other benefits, just addressing that. As the myc is growing, any "breakthroughs" to the top layer from below end, knot and leave the perfect spot for a pin to form on the coir/verm top layer.
On the other hand, if you are using just straw, the myc grows ACROSS the top, leaping and leaving large flat strands of myc that form a mat, and sucks for providing the fruiting microclimate. So casing makes a HUGE difference on straw for microclimate creation.
If you have coir/verm you get all the tiny valleys and bumps that are ideal for fruiting, so a casing layer doesn't add much benefit if your humidity is good. For pinning, there are other benefits, just addressing that. As the myc is growing, any "breakthroughs" to the top layer from below end, knot and leave the perfect spot for a pin to form on the coir/verm top layer.
On the other hand, if you are using just straw, the myc grows ACROSS the top, leaping and leaving large flat strands of myc that form a mat, and sucks for providing the fruiting microclimate. So casing makes a HUGE difference on straw for microclimate creation.