Though unnoticed by most people, the occasional one-second adjustment can cause problems for systems that require an exact, uninterrupted flow of time.
Reddit, for instance, was down for 40 minutes in 2012 when a leap second confused the company’s servers; four years later, Cloudflare’s DNS services were interrupted due to the miniscule time change.
https://www.pcmag.com/news/rip-leap-second-time-fix-to-be-scrapped-by-2035