Some of us have become overwhelmed with all the tangent types that exist when we first meet the graph editor in Maya. Knowing when to use what type of tangent and which tangent type is preferred is often baffling. However, I feel that if you understand the differences between the tangents themselves, their purpose will all become clear. The following few paragraphs describe tangent types in simple terms. I hope this is useful for those that are quietly wrestling with your anim curves.
Spline, linear, and stepped tangents are the 3 basic tangent types. One uses zero interpolation between keys: Stepped Tangents are good for blocking. Another tangent type interpolates evenly (linearly) from one key to the next: Linear Tangents. And finally, the other basic tangent smooths all the paths between keys. These are the Spline Tangents.
The Flat Tangent is good for peaks and valleys of your curves... if you want to prevent a spline value from not overshooting, you can set it to flat. This will ensure that the highest or lowest value is the highest or lowest value between affected keys.
The Clamped Tangent is a mixture of flat and spline tangents. The clamped curve is all spliney, however, there is one exception. When two consecutive keys share the same value, they will automatically "clamp" by flattening out. This is usually used for holds... like when you have a footstep that needs to stick. The foot shouldn't move from its position until it comes off the ground.
Finally, my favorite one is the Plateau Tangent type because it is like a clamped tangent on steroids. Unlike clamped tangents, it will flatten out the first and last keys. Any keys in between a peak or valley will be treated like a spline. I like to set this type as my default.
I hope this clarifies a few things for those that were struggling with tangent types. Please leave a comment if you want to discuss the graph editor further.