index feature on optical encoder

Group -
The US digital encoder on my DC servo motors (for CNC router
application) is 5 pin encoder, which includes the "index" signal
along with +5VDC, ground and channels A and B. I have a rough
understanding of the "index" signal that this is a once per
revolution signal (I think) that can be used for various functions.
I'm running these off of Gecko G320 drives with a Sound Logic
breakout board and Mach 2 software. Anybody with an idea of whether
I should wire this up or if it'll prove to be useful or not? Thanks
for any help here.
Scott