Current limiting resistor for LED for Photon


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.

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.