How much flexibility should I keep while deciding whether to pay debt or invest extra money?

Compare side by side the guaranteed after tax return from paying down the debt with the expected but uncertain return and liquidity of investing. As part of the financial analysis, it can be reasonable to split the windfall among debt reduction, reserves, and long term investing. For the long term plan, a major life event is a good reason to pause large irreversible decisions until taxes, insurance, and cash needs are clear.