[djent]

What really makes me love fansubs is when they include the honorifics when mentioning names. There's a lot of meaning that is put behind various honorifics, and that is lost when they are absent.

I'd say the largest reason to download anime from fansubbers rather than stream it is that you become part of a culture that dedicates their life to anime. It can be rewarding, time consuming, and you might end up taking Japanese classes hoping to one day translate anime and manga.

[emodendroket]

I speak Japanese and I think putting those in is a distraction. That is one of many deep nuances in Japanese that can't be directly translated into English but needs to be considered in the translation's gestalt. Your choice of personal pronoun, use of end-of-sentence particles, and choice to use polite, extra-polite, or casual expressions also conveys a lot about you and your relationship to people. However, nobody wants to read gibberish like "Boku am coming-masu now yo!!" because it's not English.

These issues are hardly unique to translation from Japanese, by the way.

[djent]

There are times when the plot changes and for example, in a romance, characters may switch from using surnames to first names. I've seen many low quality subtitles where the character will use another character's last name, but the translation will use the first name. While it does require some knowledge of Japanese (or other Asian cultures), it does contribute to the overall consumption of the anime, and only distracts from the attempted transition from Japanese culture to Western culture as translated.

[emodendroket]

I mean, that's important, but the other nuances I mentioned can change in just the same way. An adept translator can capture these things without resorting to lots of untranslated Japanese (although whether the people doing fansubs are adept is a different question... often there are quite obvious misunderstandings of what was said in the fansubs I've seen).