As the owner of a 2000+ user server, this setting is an absolute necessity because yes, disposable email accounts are plentiful and Discord still does a poor job of detecting them. Server raids still happen, and temporarily restricting access to non-verified accounts helps mitigate this.
However, Discord's phone number verification blocks most VoIP or burner numbers from being registered. It's one of the few things Discord does pretty well these days, IMO.