Extended hours let you trade before the opening bell and after the close. That flexibility is useful — earnings and news often break outside regular hours — but the rules of the game change when the crowd thins out.
Liquidity is lower, so spreads widen and prices can jump on relatively small orders. A headline that would barely move a stock at midday can send it several percent in thin pre-market trading. Limit orders become essential; a market order in a thin book can fill far from where you expected.
Used carefully, extended hours are a tool for reacting to news early. Used carelessly, they're a way to get a bad fill. Size down, use limits, and treat the quotes with healthy skepticism.