Speculative long puts: 0.50–0.70 delta, 30–60 DTE, on a stock with a bearish thesis. Behavior identical to a long call inverted. Watch for skew — equity index puts trade at higher IV than equivalent calls because of institutional hedging demand. Pay for that skew if your thesis is strong; otherwise consider a bear put spread or short call structure that takes advantage of the skew rather than paying it.
Insurance long puts (protective puts): bought against a long stock position to hedge downside. Typical setup: 5–10% OTM, 60–90 DTE, sized to cover the dollars at risk in the underlying position. Cost is real (1–3% of position size depending on IV) but eliminates catastrophic downside while preserving upside. Compare to a collar (covered call + protective put) if you want to fund the put with call premium.