I am making the jump to HD but need to learn a couple more things.
The XH A1 is in every way identical to the XH G1, except the A1 does not have the SDI, Genlock or Time Code BNC jacks that are on the G1.

What are the benefits if SDI, Genlock, and Time code jacks? Are they worth the extra cash??
If I am filming sports, races why would I need theses features?
Thanks

You probably don't need it.

SDI output is useful if you are switching HD-SDI signals (i.e. live switching). If you switch sources, most switchers need the camera to be genlocked- that is what the genlock port is for.

The other use is if you want to record the 4:2:2 signal coming off HD-SDI (less/no compression compared to HDV). This is usually impractical in the field.

The timecode and Genlock inputs are useful if you are recording double system sound and using an Ambient or Denecke box for sync.

You probably don't need any of these features.