are engines useless

Hi this article is about engines. Everyone says engines are great for improving and that you should definitely consider buying one. I do agree but take stockfish, its main feature is the analysis function but you can access good analysis even here on chess.com so why would I download stockfish when I can simply use it from a website. I've heard that stockfish also comes with a database, same thing, chess.com has about 3,000,000 games in their database and what about chessbase with 8,000,000. If anyone has any suggestions on engines with features that I can't already access or if there is something that I'm completely missing then I would like to hear them.