In some of the work I do I need to be able to correctly estimate the weight of an entire design. In some cases I need imported parts, or components like electronics or COTS parts that I can get the mass of and need to put in my CAD model (whether via import or CADing them). However, Fusion 360's current material library doesn't allow for custom mass properties so I cannot properly assign a mass to this part, thus I cannot estimate the weight of my final model.
To do this, I can go into the "Manage Materials" toolbar and create a new custom material that includes the density and properties, and calculate the density based on the mass of the real part and the volume in CAD, but this is sort of tedious if I already have the mass - I would much rather there be a button in the Material Library that says "assign custom mass" in which I could quickly type in the known mass of the part without creating an entirely new material.