He'll be paying NI at the very least. That goes towards your pension and healthcare. He'll be paying council tax. That pays for your schools and policing. He may not have any kids, he may never get ill, he may move back home before he becomes a pensioner. He may never draw on any handout from the Government.
He'll be buying things, and paying VAT on that. He'll be using local services, thereby generating revenue for the supermarket, bookie, and pub in your town. Those places then employ people.