Deep sea mining has the potential to help the global economy on multiple fronts. It will increase exploration which will require more manpower and equipment. The actual harvesting of the minerals will require a wide support group per each site. Pay scales will be in the realm of obscenely high. Although much of the profit will be reinvested, there stands to be ample return on each site so that economies will benefit greatly.
Deep sea mining will help the global economy because it will provide new jobs. These new jobs will bring an influx of spending into the economy. The new items that are mined will also reduce the cost of similar goods because of the competition. This will increase people's spending power which helps the economy.
Although as in the case of Deep Sea Horizon it may come with environmental consequences, the profit involved in deep sea mining will make it an ongoing enterprise, benefiting companies engaged and the portion of the economy that they support. They will provide employment and selling the product will put money into the economies. The hope is that it is done responsibly and environmental catastrophes are avoided.
While, initially, deep sea mining will help the global economy, in the long term it will have a very negative impact. I belive this is the case because it depends on a limited resource which we do not want to become dependant on, and it also is dangerous to the world's natural resources if an accident were to occur, which is not preventable in the long term.
Deep sea mining will hurt the global economy. I think that it will end up costing us quite a bit to even begin to get the right equipment needed to set up a system that can use deep sea mining. They will need so much material it will take a lot of money to get started.