Use grounded cords for anything with a metal case.

Yes, the third prong exists for a reason. It connects back to your breaker panel’s ground wire. If something goes wrong inside a device (like a power tool or a refrigerator), that third prong gives the electricity a safe path to trip the breaker instead of traveling through you.

Use a grounded (3-prong) cord for anything that has a metal chassis or a three-prong plug. That includes power tools, appliances, computers, and anything with a grounded plug. The cord itself doesn’t make a device safer, but it keeps the safety ground intact from the outlet to the device.

Use an ungrounded (2-prong) cord only for devices that have a two-prong plug and are double-insulated. Think phone chargers, lamps, small electronics. Those are designed not to need a ground. Buying a 2-prong cord for a three-prong device is not saving money — it’s removing a safety feature.

The only real reason to buy a 2-prong cord today is if you’re plugging into an older two-slot outlet (and even then, a $5 adapter with a ground tab often works fine). Otherwise, just get the grounded one. It’s cheap insurance.