The APC40's replaceable crossfader can stand up to some pretty brutal treatment. Not only an essential DJ control, it's also handy for controlling effect, volume and modulation curves.
In Live, you can set any track as an A or B destination, and then crossfade between A and B with the crossfader.
Normal wear and tear can render a crossfader obsolete. The APC40's crossfader is fully replaceable from the bottom of the unit, so you can extend the lifetime of this already durable unit.