As guitar repairman Dan Erlewine has discovered, "magnets are tools and they have lots of uses!" Repair shops are constantly finding inventive new ways to use them.
For example, magnets can be attached to (or inlaid in) clamping cauls for easy alignment with steel clamp jaws—a great help when aligning patches for repairing cracks, or when regluing a bridge.
An exterior magnet will move a second magnet inside a guitar where your arm can't reach: wrap the inner one in a damp cloth to clean glue squeeze-out, or attach self-adhesive sandpaper to remove dried glue.
For building or repairing guitar pickups, you can use a 1" pair to magnetize a pickup or change its polarity. Single-coil Kit Instructions tell you how.