Well, lets just say that any aircrafts parts will required to be replaced one day. Potentiometers with a brush will black spot, switches will get tired of toggling and lights lighting...
Without these great magnetic tools, all the freaking small 4-40 screws and nuts that hold these relays and gizmos would be waiting down in the bottom of the avionic bay for the next C check (or not?).
The design engineers already made our life miserable by allowing production of aircrafts without proper access panels, don't give them ideas like that!
Like a pilot told me one day:"what about solar storms?"....
