I’ve actually done this for a Microsoft owned IP before. Someone was Wordpress-scanning a particularly fragile application of one of my clients (which was not Wordpress) which was causing it to fall over. The scan stopped within an hour of sending the abuse email.
Edit to add: I used to work in a NOC for a tier 1 ISP. We had an “abuse department” (a couple people) that investigated these and opened tickets with the NOC. I’ve emailed customers and disconnected circuits as a result of abuse emails, so I wouldn’t say they’re totally useless, but I’m sure it depends on the company involved.