Just like any seasoning in food, Fe when not balanced with other things or in too high of doses tastes bad. However, in the right amount, or in combination with other qualities, it can make opinions and ideas much more palatable. Like Amargith explained, it helps match levels of emotion/sharing/feeling to what the other person/people involved feel comfortable with.
There is a huge distinction to be made between immature use of Fe and more balanced use of it. When used without any accompanying traits to temper it, it can seem either pushy, manipulative, manipulated, disloyal or it can make the user lose their own identity in the needs of others. This is often what those ardently against Fe are reacting to.
However, with judicious use and experience, it is a tremendously practical vehicle for productively expressing oneself so that the message will be received openly, being sensitive to the needs of others, being aware of what's written between the lines, and learning to look outwardly in an unselfish way (which comes naturally to none of us, whether Fe or Fi users.)
One part of Fe that Protean touched on that I really agree with is the idea of understanding ourselves better through understanding other people. When you are in the same surroundings every day, it's easy to miss the most fundamental parts of them because you never experience anything different. For me, Fe serves to look at other people and by comparing and contrasting their responses and reactions to mine, I learn to notice aspects of the "scenery" that makes up my personality that otherwise are easily ignored. This can alert me to what others find offensive in me, what strengths and weaknesses I have, and what my natural inclinations and tendancies are. Being able to do this actually (I believe) shores up Fi as well, as it short cuts quickly assessing new situations (both with myself and others) so that I am free to think about what I believe is right, or how I want to act.
EDIT: Despite being very different types of people, I would agree with all the points that Jenocyde made re Fe!