Once public, companies gain direct access to the capital markets and can raise more capital by issuing additional stock in a secondary offering. Public companies can use their common stock as currency to acquire other companies. Public ownership delivers a certain level of prestige that private companies do not have. Going public provides owners and founders liquidity for their holdings in the business. For entrepreneurs approaching retirement, an IPO makes estate planning dramatically easier and a lot more enjoyable.
Public companies enjoy a higher valuation than private enterprises.
That's less than half the public valuation, largely because there is little liquidity for investors in a private company. Public companies are more attractive acquisition candidates. For some companies, the strategy is to grow to the point where they become an attractive middle-market acquisition candidate and then to sell out. Going public usually makes you a millionaire. Even if you initially don't get the price you want, playing the waiting game can be profitable.