Sourcing rule -Planning active flag effect

Oracle user guide says as below-

If the allocation percentage for all the
shipping organizations included within a range of effectivity dates equals 100, Planning Active is checked. If the sourcing rule is not planning active, the planning process will use the rule to
assign planned orders.

Anybody can share your understanding that 'if the sourcing rule is not planning active , the planning process will use the rule to assign planned order'

here 'rule' means is that allocation % or rank or both?

planning module (MRP/ASCP)will get any impact if the flag is not enabled?

please share your observations