what are the disadvantages of not having encoder index signal on mesa 7i77 card

what are the disadvantages of not having encoder index signal on mesa 7i77 card?
I am putting a laguna cnc mill machine together and when I finally got to connect the encoder cable to the 7i77 card
I realized that I have only A / B signal coming out of my encoder, and is single ended 500 ppr.
Now what? I am going to need to change the encoders or I can still use them without Index signal
help is encouraged!
the encoder is a BEI L25G-500-AB

You can use it, of course, the only thing i know will not work without index is rigid taping, if that encoder is on the spindle. It would be nice if you can confirm this, as i am way to long without sleep so i might miss something.

That's correct, you need a spindle index for threading or rigid tapping
also for motion axis, the index allows more accurate homing

As tommy said rigid taping will not work for the spindle encoder if an index is not available. Also homing using index will not work as well. I have one encoder on my machine that the encoder does not produce an index which is not a big deal. I just use my home limit switches anyway.

I think that is the only "standard use" of index signals in linuxcnc, of course can be wrong.

My machine has Axis X,Y,and Z with single ended AB channels only. There is no encoder for the spindle yet, that I still have to get one to install it, so I will make sure the spindle encoder has the index signal in it. Thanks for the information.
In the configuration for the 5i25-7i77 does the system will keep on looking for the index signal, will this create an error? and do I have to disable the index signal somehow so the system does not keep on looking for it?

No it will not. It pncconfig will just create the links to the signal but it will be transparent to you.

This is the setup I use. 5i25/7i77.

Can give you my configuration if it would help.