There are Arduino clones that that a 5V and a 3V switch. I think this changes the voltage level of the digital output, right? So the digital output could be a 5V or at 3V.
Is that because many components, like wireless modules, use 3.3V? So the digital output on the SPI pins need to be at 3.3V level, not 5V?
Are there other implications to switching between 5V and 3V? How would one use an Arduino Uno for these wireless modules - the Uno doesn’t have a 3V-5V switch.