1. As a First Amendment matter, it affects the showing that a libel plaintiff would have to make to recover proven compensatory damages (when the speech is on a matter of public concern). Private figures may recover such damages by showing that the speaker negligently erred; but public figures must show that the speaker knew the statement was false or at least likely false. Other rules, such as those related to punitive or presumed damages, are the same for public and private figures.
2. A Texas statute offers certain procedural protections for defendants — chiefly, an opportunity for quick dismissal of cases that a court finds lacking in merit, and an award of attorney fees to successful defendants — in libel cases brought by public figures (as well as some other libel cases as well). That was the specific issue involved in this very case.