Current limiting resistor for LED for Photon

Greetings,

I’m quite new to the whole hardware aspect of development and have what some might call a few stupid questions to the Photon hardware examples page.

https://docs.particle.io/tutorials/hardware-projects/hardware-examples/

Looking at the “Blink an external LED” section of the link above I’m wondering why it states “When using an LED, you must always add a current liming resistor. Normally you’d use a 220 ohm resistor (red-red-brown-gold) for 3.3 volt circuits.” - seeing as my Photon seems to output 3.3V and the “standard” forward voltage of a LED is also 3.3V, I can’t see why I need a resistor. What am I missing here? If the voltage didn’t match I could of course calculate the needed resistor.

Additionally the guide states “It’s good practice to connect the red (+) bus bar on the top to 3V3 and the blue (-) bus bar on the bottom to ground” which seems strange when I look at the images below the text where the red bus bar seemingly isn’t used.

Hope my beginner-questions make sense.

/Mads