You can find a good write-up about it in Tompkins "Secrets of the Soil."
It's important to note that for agnihotra to have any chance of being
effective, it has to be practiced at exactly sunrise and exactly
sunset. Even dairy cows are more forgiving.
In my experience, any benefits from agnihotra have been too subtle to
identify.
I think it's probably a great ritual in a spiritual community with
lots of people who are looking for a way to fill time. (I'm saying
this seriously!)