USB 3.0 standart is meant for PCs/Macs/Devices. Original USB 2.0 port on PC would output only 0.5A. Default wall chargers would output 1A. Car chargers are different, but my 2A charger didnt charge my old phone any faster.
With USB 3.0, PCs should give out 2A (if Im correct) meaning u will charge 4x faster on USB 3.0 port.
With wallchargers its different. Cable itself doesnt have the limit (atleast not noticable one), meaning on 2A wall charger, and stock USB 2.0 cable, which comes with galaxy S5, you should charge with 2A.
Each device have power protection aswell, thats why older phones can use max to 1A to protect itself, while tablets needed 2A charger. I suspect galaxy S5 is made to charge with 2A aswell, aswell it holds up backward compability with 1A.