Because of the magnetic resistance there is some energy losses
Unexpected heavy load may cause the coupling to slip
ferrous particles in liquid are problematic when you are using magnetic drive. This is because particle collect at impeller and cause the stoppage of pump after some time
- See more at: http://www.green-mechanic.com/2014/05/advantages-and-disadvantages-of-centrifugal-pump.html#sthash.Oe1M3aEd.dpuf