We often use the power supplies like batteries or direct AC/DC supply which are normally in higher ranges compared to the actual requirement for the circuit. In that cases we need this kind of voltage regulators which can regulate and vary the voltage levels for the circuit requirement.
The AMS1117 series of chips are linear voltage regulators with low voltage drop. The modules based on the AMS1117 chip provide constant 3.3V or 5V outputs from an unregulated DC input. It's very compact and can be included in your project schema or you can use it together with a breadboard for circuit testing.