It allows their financial partners, who were shorting the stock, to buy stock at a cheaper price, thus mitigating losses, so instead of say potentially losing 5 billion, they'd lose 2.5 billion (this is merely an example with made up numbers)
This is, however, clear market manipulation, and highly illegal. Senior House and Senate officials from both sides of the aisle are now calling for an investigation into the companies that halted buying GME stock.
In other words, this is not gonna end well for the hedge funds that were involved in this.
There is a chance that the government is gonna crack down on these hedge funds, and that at least 1 is gonna completely go bankrupt.
On a side note, Citron is already declaring that they'll no longer be in the business of shorting, and will refocus on day trading. In other words, the risk of shorting a stock has gone up substantially, due to the existence of entities that WallStreeBets.