For a sense of perspective, it's about the signal to noise ratio. Recruiter spam can be as bad as any other kind of spam if it gets to a high enough volume to overwhelm your inbox, especially when you aren't looking, or when they're way off base. For instance, if you're an architect who designs buildings and the recruiters are trying to offer you software architect positions. Not sure why these recruiters think they're adding value here.

Personally, I set up gmail filters to auto-archive all emails from LinkedIn.

Its only a feature if there is a sufficient amount of work one is interested in and a good chance that the recruiter can match you to a job. In my experience, there is a lot of garbage because recruiters throw a wide net without considering whether the job is a good fit.