These covers allow for hidden cable routing for wires going up the Z Extrusions, they also have a cutout in case you didn't leave enough room under the Z Rails(most people don't :P).
In case you want to add some extra pop to your covers, you can swap colors between layers 3 and 4, which is enough to look good on the top, but would make only the top surface a smooth looking piece, while you'd have a pretty noticeable color difference when looking at the sides.
To remedy this you can either color change between layers 4 and 5, leaving a single line on your covers, OR preferrably change the filament after doing the bridging section on layer 4.
Pictures courtesy of jmaurin#7720, over at the Voron Discord.
The author remixed this model.