Voltage is a measurement of the force that causes the electrons to flow in a circuit. That’s the definition. I don’t know what that means either. In 38 years, I’ve never seen an electron flow!
Most technicians use 12VDC and 24VDC transformers and Power Supplies to power their devices. 1 or 2 batteries are added to power supplies for battery back up if needed. Transformers have no battery back-up.
The voltage requirement of the hardware you’re powering determines which voltage to use. It’s that simple.