A value of 0 makes this object static and fixed (also in mid-air, this is neccessary even when the object is Static with its Motion System set to Fixed).
A value of 100 makes the object too heavy to be moved by the player.
Mass & Damping
For damping, mass is also important, this is due to the mouse not "using force" to move objects, but Oblivion using the mouse movement to calculate the force needed for an object to move the same distance the mouse pointer did. So, to make objects draggable smoothly, you have to use a high mass value and a low damping factor, usually 0.1 for linear and 0.05 for angular damping.
The object's Mass seems to be the only collision data that can be change in-game via script or console.