Instead of getting welfare checks, unemployed folk get jobs. They learn skills, help restore our infrastructure (great for businesses) and by making a living income (rather than just subsistence support), they pour that money right back into the economy, which again is great for business.
The biggest long term upside is that the only “profit motive” is to our society as a whole, rather than the bottom line of a major corporation. A large percentage of the infrastructure we have now in the US that is crumbling was built by the WPA and CCC. Right now would be a great time to renew it (and then we should maintain it — much cheaper long term).