As far as i know, the fan on the left is for the CPU and the fan on the right is for the GPU.
This would make sense when gaming that the right side gets hotter as the GPU is under more stress.
ASUS ROG G750JH -T4024H
CPU: Core i7 4700HQ 3.4GHz
GPU: 4GB NVIDIA GeForce GTX 780M
RAM: 32GB
STORAGE: 1TB HDD + 256GB SSD
MONITOR: 17.3" FHD (1920 x 1080)
OS: Windows 8.1 PRO
Lovin' this sh*t