Hi @Jonas,
We use Reusable blocks for any reusable page content that we or our clients need to drop into a page that can be edited in a single place and have those edits update all instances of the reusable block on any page it is used.
Examples: FAQ section, customer logos grid, newsletter sign up forms, etc.
We use Block Patterns for any reusable content templates that we or our clients can use as a starting point where each instance can have unique content.
Examples: Headed content, CTA box with action buttons, side-by-side text and image content, etc, etc.
We use Template Parts / fragments for any site content to be used to arrange pages and/or be selectively displayed on pages via the Cwicly Themer visibility conditions.
Examples: Headers, Footers, CTA sections, Banners, etc.