I had got 2 purposes for buying ETH:
1)  I always use ETH for buying ICO (small) because, as you know, many projects currently based on ERC-20 platform. In the past, many ERC20 ICO has been pumping strongly and I think It would happen in the near future.
2) I trade ETH in short term, sometime is day trading, or buy other altcoin by ETH (sometime you can buy Altcoin by ETH with very cheaper than you buy it by BTC )