To locate any vertex, it is spatially described with x and y coordinates - of course. You can also add Z and M values - but what is the advantage to use the Z in the vector instead of a attribute Z in attribute table?
In which cases should I use the Z values instead of just a attribute: "Z"? For me it seams easier to use a Z-attribute field because I can use it in expression dialog like any other attribute. Also if I want to make a 3D-looking map, the 2,5 D symbol style asks for a attribute field not the Z-value (screenshot). Also qgis2threejs is asking for an attribute to draw the height of a building...
Screenshot: The Identify window shows, that my buildings already have a Z value. It's written from the "_mean" attribute by using the tool: 'Set Z value'. The "_mean" attribute was created with 'Zonal Statistics' from a DSM (LiDAR). The "2.5 D" symbol needs a height but can't uses the z value, so I have to use the attribute "_mean".
I would like to have some cases or examples where the Z value is needed.
What are the advantages of the Z value?