What is the correct way to create and insert blocks in regard to layer zero? Create them on layer zero (0)? Don’t create them on layer zero?
My answer: Just understand what is happening in each scenario.
AutoCAD Entities (commonly referred to as objects) reference both the layer(s) they are created on (the layer the object is on when you block it) and the layer they are inserted into when brought back into the drawing (inserted into their current residing layer).
The Layer Objects Were Created on Takes Priority Over the Inserted Layer
If you turn off or freeze a layer that an object was created on, then the display of that object will disappear. But if you turn off the layer the object is on, it will not; the layer has to be frozen in order for the block to disappear.
So is layer zero different than other layers? Yes, layer zero does have a unique ability that other user-created layers don’t have. If you create an object on layer Zero, it will NOT reference that layer (0) when inserted on a different layer. So freezing Layer Zero (0) will NOT remove the display of the block.
So now only the layer the object is inserted on will remove the display of the block when the layer is frozen. Simply turning off the layer will not turn off the display of the block.
Study the settings and display(s) of each of the 4 sample blocks. (Blk is the referenced layer and Ins is the inserted current layer.) Colors and other properties work the same way; the layer they are referenced to takes priority over the layer they are inserted on.
The property will only change if the reference layer property changes, unless the object was created on layer Zero (0), in which case the inserted layer takes control.
Blocks can be mysterious, but how they respond is all within your power.