Others already mentioned benefits for us currently living humans. Long term it is also interesting from an evolutionary aspect. Humans communities on earth are

Others already mentioned benefits for us currently living humans. Long term it is also interesting from an evolutionary aspect. Humans communities on earth are less and less isolated from each other, making it near impossible to evolve in different directions. That increases the risk of getting stuck in a bad local optimum. Gravity well's are an isolating factor. Living on mars will require a highly isolated economy producing essential goods. Once that prove of concept exist can it be reproduced everywhere else in the solar system (or beyond). Those communities would not be subject to many of the tragedy of the commons situations we have here on earth with our shared ecosystem. No climate change. No plastic in water. No gene manipulation. Hell, you can even build a space station for only white people, if you are into that. Down the line, we'll see what works best. Earth being that highly interconnected / -depended makes it more peaceful than ever, so war might become a problem again. Communication is still somewhat easy, so working together will likely still be beneficial.