Today is a two-fer. Ever wonder how soft aluminum is? Well, here's two examples why you have to treat alum with a little care.
Exhibit 1 - Shoe rub has worn these aluminum crank arms severely! Apply a little too much power and you risk snapping one off.
Exhibit 2 - Cable rub can do a lot of damage in a short period. This is why it's a good idea to protect your frame with some protective tape.
Exhibit 3 - Exhibit as an exhibit.