Investor goals and founder goals are rarely aligned. If you want to go for world domination and would rather risk everything to achieve that and possibly end up with nothing at all then go the investor route. That will increase your chances of ending up with nothing, but it will (perversely) also increase your chances of success. If you're already happy at your current level just grow it organically and don't look ba…
take note that the slow/"safe" way also has its own risk - that someone will discover your currently-secret goldmine and overtake you due to having more resources/connections/investment.
But that risk always exists, even for funded companies these risks are present. It's an arms race and if your opponent reaches for the nuclear option you have to be very patient and stable if you intend to wait them out and they may even succeed.