IPOing a state corp will sell shares of ownership to other players or the game-system (in the form of Investment Funds).
Pro: You can raise cash for your country treasury by selling shares in profitable state corps. These corps also tend to run at higher production, generating higher corp revenues.
Cons: You're selling ownership in the corp. So the profits are split between you and whoever buys the shares you sell. If some other player (not an investment fund) acquires a greater share of the corp than you, they acquire control of the corp, and will manage it thereafter. (You'll still retain your part ownership.)