Reduce work and hence let someone else work for him (increase employement)
But that won't necessarily work. Say the person is Bruce Springsteen. He's making enough from royalties to hit the max. So he doesn't need to tour at all. But if he doesn't tour, there isn't necessarily someone else that can tour instead of him. It's just as likely that his fans will just stay at home and play recordings.
Even worse, remember that a Springsteen concert involves many other people that either don't make money from his recordings or not as much:
- His band mates. He's the face of the band and may well make the largest share of the proceeds.
- Roadies. They make no money from recordings and are only paid for their duties on the live show.
- The venue crew. Ticket sellers, concessions, security, cleaning, etc. None of these get any money if he doesn't play live shows.
Beyond that, there are ways to get around such a limit. Instead of buying things with the currency, barter your services directly for what you want to obtain. Or have your employer pay you in benefits rather than salary. So you and another person may have the same salary, but she or he gets driven to work by a limo paid for by the company while you drive your own car.
Spend more money so he/she can keep up his/hers income (boost economy)
It seems unlikely that most rich people actually keep large cash balances. They either invest or spend their money already. So any boost from this is going to be minimal. Another problem is that this boosts the effective money supply, which is going to cause inflation. So the government will print less money in response, which of course removes the boost.
Profit from social security, since increasing cash flow leads to (possibly) higher tax-income.
This seems unproven. As I said earlier, it could just as well reduce employment.
probably get faster a new job, since profitable companies can only spend more cash on either assets or empolyees
This doesn't follow from what you wrote, but let's assume that you do something else to make this so (e.g. limiting currency accrual of companies as well as people). Then how do companies get investment capital? If they can't pay dividends, then who buys stock in the company? How does a company start and grow? Realize that many companies have a minimum size. FedEx is one of the most egregious. They need to be nationwide. They don't work as a local concern. But other companies have a similar problem. You can't build your own car and sell it to compete with Ford. It would take one person years to manufacture a car and how would you pay for parts and materials? Design?
So instead of getting a new job faster, this would mean that new jobs would be quite rare. You can only get a new job if an existing company expands. And it could only expand in fits and starts. They'd have to buy land on the layaway plan. Then put up the building in fits and starts. Buy one machine here and another there. Then, after months or years of preparation, they can finally start hiring employees.
Under this rule, a company can't save for a rainy day. So if business is slow, it might go out of business entirely. All of its employees are laid off. The best find jobs quickly, possibly displacing other workers. The lower quality workers stay on the job market.