The description given for the Delta Mode in the product rule varies in two places.
In CSSA content (https://academy.pega.com/topic/configuring-product-rule/v1/in/2866/5371) it says as "Select Delta mode to include only the highest patch version of the application's rulesets in the archive file. For example, if your application references OrderEntry:02-03-05, the archive file produced from the product rule includes only rules in OrderEntry:02-03-05. This feature is useful when you are migrating a patch update."
Thank you for raising this. Both sources require some updating to be accurate. The content on the community (PDN link) is close but the opposite is true. Checking the Delta mode check box includes only the current version of the application. Deselecting it (unchecked), includes all versions of the application which is also more intuitive/consistent with the name since the idea of Delta is to only refer to changes. You can test this by creating a higher version app rule and corresponding rulesets. Then save a rule or two into the higher version ruleset. Create a product rule referencing your higher version app rule and toggle the delta mode on and off. You'll notice a significant difference in the number of rules included when previewing the product rule.
I've made a change request to update both the Academy and Community content to reflect this.