It has a good and bad effect in the marketplace when it come to the price of bitcoin in the market. If we mine all of the bitcoin the supply will surely going down and meaning I guess the bitcoin price will rise also there is a high percentage of bitcoin that is lost from a forgotten wallet address that will never be recover again that is also a big contribution in the market. The more of the investors in bitcoin the higher the bitcoin price will rise having the bitcoin price rise is a good thing but if it doesn't regulate it might have a bad effect in the community.
Close to 1,000 coins are being mined per day as of now, and this will decline to around
BTC500 per day after the next block reward halving. However, if you compared the daily volume, these numbers look minuscule. According to coinmarketcap, the 24-hour trade volume for Bitcoin was around $25 billion. And the value of 1,000 BTC which are mined every day comes to just $9 million (less than 0.1% of the daily trade volume). So I don't think that the block reward halving will have a major impact on the exchange rates.