The state corp. has to have enough money to buy resources and pay its workers (of course). I use 80% on mine, but I have a 0% tax rate. A good guideline to follow is to have your tax rate and profit sharing equal 80%. (There are other ways that work just as well).
If you have your profit sharing too low, the game will automatically transfer a percentage of the profit to your country. The game will keep 50-60K on hand for the corp.
I hope this answered your question.