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In Speed mode, you start with scope (what projects do you work from) and tell Structure what you want to see on every level of your hierarchy (issue types, groupings by field, etc.).
In Power mode, you can build structures by hand or using generators (rules for inserting, grouping, and adding related issues). In Power mode you can also add static folders flex items, which you can use to group issues. If you've been using Structure for awhile (on Jira Cloud, DC, or Server), you've been using Power mode - it just never had a name beforecan be used for project planning or grouping issues.
All other functionality (adding columns, sorting columns, formulas, quick filters, etc.) works the same, regardless of the mode you selected.
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