What can you do with a PBE account?
PBE lets you preview new champions before they hit live servers.
You also see new skin lines (Star Guardian, Arcane, etc.) ahead of release.
Item changes, jungle reworks, and major patch overhauls are all testable. Riot drops experimental modes onto PBE too. Some make it to live; some don't. For coaches and streamers this is invaluable. You record content on upcoming champions before competitors. You build matchup intuition before they hit ranked.