They no longer work as well as they used to. When we started prospecting for our consulting business in 2014 we got a nearly 50% response rate, using a specific "research driven" template. We frequently had people comment on how good the email was. Now, that same email barely gets a 10% response so the tactic is not worth it and we have since found better ways to reach potential clients.
Also, at the time LinkedIn didn't count emails that got no response against your limit, so you could get the starter premium account and send lots of emails. Now, they have reversed the policy. Emails that get a response don't count towards your limit (because they were relevant to the recipient).