Advantage to Upgrade

Apple leaves the past behind quite quickly. Support is for the current and last versions (now: Sonoma and Ventura and Monterey). Innovative features are only for the latest OS.

If your machine can run the latest version, and you have no known requirements that hold you back (e.g. software X is essential for you, but their developer says that it doesn’t run (well) beyond Monterey), then I would advise to keep current.

The first that some users of old OSes may notice, is that Safari isn’t updated anymore, and modern websites may malfunction. Monterey isn’t in that danger zone yet, but it will happen at some point. Firefox and Chrome may bring web tech support a little longer, but eventually they will also stop releasing for older OSes.

Here are all the new features you'd be getting: macOS Sonoma - Apple. Updates also include security updates and bug fixes.

Pros: You'll get all of the new features in macOS Sonoma

Cons: You'll also get all of the new bugs in macOS Sonoma. Some of your 3rd party software might not work. Your computer might run more slowly.