GTX 1070 is a poor choice for mining as it costs about 2x vs many RX 470 and some RX480 cards, but mines about the same hashrate.
The only reason I have a BUNCH of them is that my intended usage for them isn't mining - they're just mining to help pay their cost while the mining is profitable.
A GTX 1070 is very good card for gaming and mining as a hobby.
For a gpu farm, semi professional mining, amd card are a better choice (less expensive -> less initial investment, similar hashrate on most important algo, but higher power usage, better ROI).
A small miner may aims at less popular coins, without pools or big exchange and have a higher profit per card.... A gtx 1070 is very good for spreadcoin for instance (a small interesting coin on bittrex with low volume), or lbry ( not a small coin).