Changing the default from 10 to 0 would give projects by default a higher priority in autoscheduling
This change won't change the indicator color next to the Priority on the project page(s) it's set on (such as Project Properties) out of the box as both 0 and 10 are green (High)
See Display mappings below:
Additional Information
See KB: 141061 for tips on how to optimize use of Self Service for Clarity PPM