RCA is done by sending a signal over a coax wire. The shield is the ground and also protects against outside interference like EMI/RFI.
As the RCA only standardised the plug, voltage can be anything.
Balanced also use a shielded cable, this time with two signal wires. The hot and the cold. The latter is de inverse of the hot.
At the receiver, the hot and the cold are compared and any difference is removed (common noise rejection). This makes is an ideal connection in a electronically dirty environment.
When implemented properly, the ground is a true signal ground, preventing ground loops . Practice might be different.
Voltage is higher. 4.2 V is the minimum. This allows for driving long cables.
As my DAC has both RCA and XLR, I could compare them. Didn't notice any difference. I run the XLR simply because it is rock solid.