I'm building a Pandora device based on the Pi which uses the P1 header with Adafruit's Pi T-Cobbler breakout.
The 3.3V pin (P1-01) powers 6 momentary buttons each with the following circuit:
The 5V pin (P1-02) powers an LCD through the following circuit:
So the question is: is there any reason that I should use different ground pins for the circuits on the two different power rails? For example, should I use ground pin P1-06 for the buttons and ground pin P1-09 for the LCD circuit?