Every electronic circuit needs to be powered. The choice of electronics power supply is a design decision you will make with every electronic circuit. Three types of electronics power supplies are common direct to power source, linear and switching. Each has its advantages and disadvantages.
Direct to Power Source Simplest and cheapest since no electronic parts are required. It can also supply quick surges of current.
Batteries are unregulated and their voltage goes down with usage. Your circuit must be able to tolerate this wide input voltage range. Use a brown out reset feature to prevent data loss on microcontrollers when using this type of supply. A brown out reset is a good idea in any case.
They are commonly used in toys and in powering the Power Amplifier section of radios.
Linear Power Supply Simple and cheap. Good output there with little ripple.
However it dissipates power as thermal heat so it is not efficient. The power wasted as heat is equal to
Power dissipated = (Vin - Vout) * Device Current
Thermal issues become a problem if there is a big difference between input and output voltage.
If you want to use a linear supply with big difference in input and output voltage, consider using a resistor in front of the linear power chip to dissipate some of the heat.
Switching Power Supply These are slightly more complex. They work by chopping DC into AC and then using transformers to change voltage levels. The resulting AC is rectified to produce DC. They usually achieve efficiency between 80-90%.
There is an output ripple that may be a factor for sensitive circuits. The ripple can be lessened by putting a linear power supply after a switching power supply. A common configuration is to use a switching power supply to generate output voltage a few hundred millivolts above the voltage required by the linear power supply to give regulated voltage.