The S4 cable (with original charger) can do 1900 mA, but if I use one of my other random cables, it will vary from 500 -> 1200 (with my S4 - not a Moto G!). I think there's some physical differences to this cable than normal ones to enable this. Found this wee thread on XDA on S4 charging - http://forum.xda-developers.com/showthread.php?t=2274321
The main time this will make a difference is (IMO) when you're using GPS and even though you're plugged in to the 12V socket, your battery will drain.... Unless on a good quality charger + lead combo.