Trying to understand NEO/ETH fixed/growing circulation

[Breadwinner]

Going forward with my altcoin studies and trying to understand NEO and Ethereum better. Could I get few things clarified:

- I've understood that you cannot compare ETH & NEO to bitcoin directly, since BTC is a crypto currency while NEO and Ether are platforms. And inside those platforms can then exist many different projects. My question is: why does NEO have fixed circulation supply, but you can mine Ether. What is the exact benefit of this. I understand how mining works for example in bitcoin and they are basically running the show. if you don't make it mineable is it so from the platform/currency controlling reasons?

- If I've understood correctly, you'd see ETH and NEO more like traditional stocks, which then pay this GAS sort of like divident. I have a NEON wallet where I have some NEO and then it's accumulating gas. When I made transactions to/from bitfinex I noticed there was no cost. I understood this GAS is used to these smart contracts (which I'm not so familiar with). If I don't care of any smart contracts and I just want to HODL my NEO til eternity - what is this GAS really good for. I just HODL it and sell it too one day?

- I have Exodus wallet which supports many altcoins including Ether. I have few Ethers there and sometimes I have NEO and Ether in an exchange if I'm selling/buying. If I have them in a place which doesn't have gas support, does it mean then that it goes to the exchange/wallet developers?