Are you thinking of people who are new to anime? As a foreign language teacher, you are used to students who are not fresh into the material before some of the harder translations get started. Of course you don't want a literal translation because they end up sounding wrong. But sometimes the only way to figure out what you need to translate it to is by first doing a literal translation. I took Latin for 4 years and there was no way I could have figured out some of the poems without the aid of the literally translation I did moments before.

Not everyone knows what Shinigami are. I know I didn't for years. Notes do solve these problems and I truly prefer them over literally translations, but the fact of the matter is, I don't really want to have to constantly test my Japanese knowledge when watching the 14th eps of a series, after the notes have stopped or worse, having to look at the same note for the 400th time. Notes clutter up a lot of space and after a while, you DO get tired of seeing one you've finally learned.

I really don't like looking at fansubs that are 70% Japanese (I've seen some naruto ones like that). THAT takes considerable effort to mull through and sorta destoyed the enjoyable experience of some of those eps. Most fansub groups don't Americanize, they just take a lot of phrases that don't necessarily have english or western analogs and turn them literally (which is the best for those situations in order to not alienate new watchers).