Is 'fd' partition type of any use ?

Hi,

it is not clear to me if 'fd' partition type is of any use for building
a md raid array. I am under the impression that this is only a legacy
trick that is not necessary anymore.
But most information regarding md raid on the net seems to take for
granted that 'fd' partition type is mandatory.

man md or man mdadm or not so clear to me regarding the subject.
So, where is the truth ?

Thanks,
Franck