Using the enclosure alone without flyleads can be bad depending on the construct of the enclosure/board, if you are terminating to a removable gland plate of a any metal that is not a solid part of the construct then a fly lead is needed as you will be relying on the (usually) self tappers that affix the plate to the rest of the box and you cannot say for sure if these screw which are usually paint on paint contacts will carry a fault current.
(There is nothing wrong with looping fly leads as long as its CSA can serve the largest circuit.)
This is why you don't need a banjo on metal conduit through boxes because they are a complete solid mold yet most gland plates would require them to ensure good earth fault return.
I would also add that even when glanding to solid constructs then without a flylead you have to ensure good contact and not poor contact to paint, IE using robust serrated washers or removing the paint prior to termination.
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