Thinner: When you 1) want a quieter GPU, 2) are too cheap/lazy to water cool, and 3) have an itx case that can't fit a 2.5 slot card without an unsightly bulge :
Only Nvidia's RTX 30 Founders Edition GPUs will have dual axial fans and 12-pin power cables | Rock Paper Shotgun
Dual-fan GPUs vs. triple-fan GPUs: Which is better for gaming in 2022?