Main Spark Bias advice needed

[Kitch]

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°.

[delcowizzid]

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

[Kitch]

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?