How strange. I was discussing this very topic via PM with somebody yesterday. It was mostly focused on the difference between Fi and Fe.
I said I found Fi to be scary because it's just too damn conclusive for me. Too black and white. I feel the world is just too complex to see things in terms of just right and wrong. Fi values just seem so set in stone and impregnable.
My friend said that Fe is scary because it is flexible. Fe seems too bent on changing to please the mood of the moment.
I would say at its best that Fe is adaptable values and its purpose is to seek the greatest harmony for the greatest number of people. In fact, I feel great discourse with those whose values lie outside of the general population's acceptable values and who refuse to compromise even a little for the harmony of everyone.
Whereas Fi at its best is a passionate vision of what is the best values for everyone (or just for that individual). It stands by that vision, even at the sacrifice of harmony.
Te and Ti is much simpler.
Te is organizing, building, ect. Ti is defining, clarifying, ect. I like to think of it as Te is glue and Ti is a razor.