Assuming you're using GitHub: a draft PR has a comments thread, which you might choose to keep after merging; it can have linked issues (that close if the PR is merged); the draft PR is organised in the list of PRs so it has higher visibility than a branch (some projects have hundreds of branches but few draft PRs) and a more clearly presented one-line description, and you can promote it to a regular PR while keeping the comment history.
Overall theme: With a feature branch, you'll need to announce and discuss it somewhere else. With a draft PR, those are features attached to the PR.
