The post formats are in a way left over from WP before about 2012 or so. Before then, most themes supported post formats that would format each type a bit differently. I’m not sure what year it was, but at some point the WP “twenty-something” default themes stopped supporting post formats completely. But Weaver’s roots still go back to before that happened, and for compatibility, we’ve not been able to drop that support. So they are a bit of a legacy feature, and pretty irrelevant given page designers and the block editor.