Main Spark Bias advice needed

What do most people here do with there "Main Spark Bias" scalar value?
I searched a bit and it seems like quite a few people just zero it out, what's the main advantage to 0° as opposed to just leaving (in my case 9.8°)?

I can see how changing the value to 0° instead of 9.8° automatically adds 9.8° to my "Main Spark Table vs, MAP vs, RPM" values.
In my case that changes my Main Spark Table from 12.3° 3600 @ 100 KPA up to a better looking 22.1°.

Spark biases are so the processor can do minus calculations as it can't do minus numbers .so things like air intake Spark retard tables etc can subtract timing

Thanks for the reply, I've read that the Main Spark Table can't have negative numbers in it and I can see why the factory has bias values to help achieve that.
I'd like to know why it seems quite popular to just zero it out?