If I just want to connect LEDs to the +3.3v pin and ground pin, what limits the number that I can connect? For example using green LEDs with a voltage drop of 2.2 V, I can only connect one with a resistor in series, because 2.2 + 2.2 V > 3.3 V.
But, in parallel, what stops me from connecting many LEDs? The voltage across them will always be 2.2 V, which is less than 3.3 V?