Fairly new to Kicad and have created a few schematics over the past few months.
I thought I understood bus wires. They are used to link up wires and I’ve always included them in diagrams.
Today I was busy with a simple schematic and left off the bus wires but still had the labels on the wires and everything passes the ERC andeven in the PCB layout the rats nest shows the wires with the same labels connected together.
Pin 6 on U2 shows its connected to U1 pin 1 & 2…etc.
There is one exception to buses being simple graphic lines. You can connect a bus to a global label or a hierarchical sheet pin instead of using multiple such labels. This works if your bus connections are of the style common_prefix# (with # being an integer) you can then use labels of the form common_prefix[1…n] to connect a full pus via them. (In future it will be possible to do the same with named signals on a bus.)