Anything that cares about really small timescales would have issues. UTC and TAI seconds, microseconds, and nanoseconds are always the same length. UTC has leap

Anything that cares about really small timescales would have issues. UTC and TAI seconds, microseconds, and nanoseconds are always the same length. UTC has leap seconds to account for the change in rotation of the Earth. TAI just doesn't care and keeps chugging. UT1 instead varies the length of the second so each day contains the same number of seconds. The variance would be less than 12ppm (1mil/seconds in a day), but some applications like navigation would have issues. EDIT: Most computers end up using a modified version of UTC where the leap second is smeared at the NTP level instead of explicitly experienced. So any computer that uses that could probably use UT1. But we couldn't use UT1 universally.