Aerators are small attachments that screw onto the end of many taps. They mix air into the water stream, reducing flow without making it feel weak. You get a softer, more even spray instead of a harsh jet.
This means less water used for the same tasks—washing hands, brushing, rinsing dishes. Bills can drop slightly, and if your area has supply issues, it helps stretch available water.
The stream also splashes less in many cases, making sinks less messy. Simple swap, noticeable comfort improvement.