There are a lot of noticable and conflicting practices in subtitle translations. What tends to bother me is deviations from what is said in English (I use subtitles all the time). It’s clear the same people didn’t work on it.
For language studies I might switch the audio and subtitles to different settings as a way to build vocabulary. Inconsistencies with honorifics in Korean and formalities in Chinese do come up a lot. In Romance languages it’s sometimes odd to hear people speaking informally to everyone - bosses, cops, clergy, older strangers on the street, etc. It’s only in Korean that characters chastise each other for that particular breach of etiquette, though. 
