This is strictly my opinion on the matter however little informed it may be..
When the poor and middle class have money to spend, they are forced to spend it. They need to buy things constantly like healthcare, food, child costs, housing, electricity, etc.
When the rich have money, they aren't even inclined to spend it. They sit there with bank accounts (not investments) of millions. This is just money sitting there. Rainy day money.
When the poor and the middle class "save" they save to spend it on a car, or a house, etc etc, and they only save a couple hundred thousand, or even much less. The rich save millions and the business owners send money out of the country to holding havens like luxembourg, belgium, and the caymans, and pay very little on returns. So not only does the rich being richer not improve the country strength as much as the poor having money does, they're not contributing a fair amount of taxes either.
tl;dr
Poor and middle get more money: Spending increase across all sectors, strenthen national power, increases in investing, greater local wealth, increase in market competition, gentrification, large tax revenue.
Rich get money: Increase in luxury goods purchasing, same amount being invested (if money is earned investing without actual growth, it is earning at the expense of others), reinvestments into corporations, lower sales and income tax earnings, increase in nepotist tendency
