I think OP is referring to the widely used CAT (computer-aided translation) tools that save every sentence you translate into a translation memory (XML file, known as TMX, usually) to be auto-inserted when those sentences (segments) re-occur. It can be a huge timesaver. Sometimes identical segments need different translations, so they still need checking.

Most of these CAT tools integrate machine translation at some level, either through their own engines or APIs. This is traditionally to save the translator time on the simple segments (numbers and their formatting, lists of countries, place names etc.) but can also be good for avoiding multiple dictionary lookups in unfamiliar fields. Obviously professional translators should avoid working in fields they are unfamiliar with, but there are always new terms and technologies to contend with.

https://en.wikipedia.org/wiki/Computer-assisted_translation

As for the incremental improvements decreasing, that's a tricky statement to make with AI/MT creeping ever more into the software translators use daily. Might be more representative of OP not exploring all new features in the software they use.