I'm very new to Arduino and was wondering if you could use a toggle switch to turn an Arduino. Obviously, I could put the switch directly in line between the Arduino and its power source, but that doesn't work if I wanted to use USB. I don't have to power it with USB so it's not hat big of a deal.
Yes, you can use a toggle switch to control power to the Arduino.
If the Arduino is put in a case, you can add a switch between the Vin pin and an external power supply, 7.5V works well.
Depending on your application, you could leave the actual board 'powered up, but use the switch to put the program into deep-sleep or wake-up as needed.
The sleep current is minuscule.