It's a hassle for anybody doing or recording "physics" as they cannot log against UTC (which may or may not have an added second or removed second in some interval if it happens to overlap the adjustment zone).

Those things that really do rely on actual "elapsed time" rather than the difference between two recorded "book times".

Does this happen? Yes, a few times in my career in geophysical exploration - it's why multiple bits of gear are synced to a reference "real clock" which gets logged against the raw GPS epoch time (real time since Sunday last week(?)) and processed "UTC" time (some variation of it).