"But, considering the limited military impact, why does Hammas allow them to continued to be fired, for what benefit, and who benefits?"

The benefit is the widespread opprobrium that befalls Israel when it responds. As demonstrated on Mudcat there is no shortage of those who avail themselves of every opportunity to heap hate on to them. As shown in Richard Landes' videos, Hamas are quite skilled at orchestrating atrocities for which there is no shortage of dupes ready to buy into. This confers on them a folk hero status among thir neighbours - you know the "standing up to the little satan" routine. It also increases the financial aid they receive from their proxy master, Iran.