What are the Advantages and disadvantages of permanent magnets?

What are the Advantages and disadvantages of permanent magnets?
permanent magnets and wound stators (temporary magnets) can be used inthe generators and motors.
in small size generators (eg: dynamo in cycle),permanent magnets are used because,
1 it does not require electricity to magnetise
2 does not require stator cooling
but in larger size generators and motors, temporary magnets are prefered because,
1 it is small in size of same power permanent magnets
2 we can control the stator magnetic field by adjusting the power
3 the magnetic flux density per square cm is more
etc..