I believe the concern is that the coiled portion remaining on the reel, when 'energised' will produce a magnetic field... Google "degaussing coil" for an explanation. Due to this generated magnetic field, heat will be generated and
has the potential to break down the insulation. The produced magnetic field also
has the potential to bugger up electronic devices (mobile phones, pacemakers, etc...) if too close to the coil.
(Navy dit

) I remember jury-rigging such a coil to degauss radar CRTs and bridge displays after the ship had transitioned the equator as they'd gone all 'wonky'. Worked a treat!