In some instances I can see the advantage of fretted fiddles. Mark Wood, maker and performer makes them for his electric models.

There are reasons to use fretless and fretted basses so why not fiddles as well?

The fiddle is one of the hardest instruments to play because it requires hours of practice to get the notes in tune. For those who transfer their skills from mandolin or guitar, the fretted fiddle can help get quicker responses in intonation.

The biggest drawback I can think of is the tone production which may be affected by the frets.

Being purist about the fiddle makes no sense. It's an expressive instrument capable of lots of different musical styles and this would affect the choice to go fret or fretless.

If the goal is to master intricate melodic lines quickly, I would think that the fretted fiddle would make sense.

In limiting the instrument, an analogy would be not wanting the guitar to be anything but played in a classical style with nylon strings and held between the legs.

I think if a person started with a fretted fiddle and then if needed could graduate to fretless when the fingers have memorized their positions on the board. Painting fret positions on the board rely on visual rather than tactile approaches, not the fastest way to learn. Muscle memory is the chief ingredient to learning an instrument.

Mark Wood uses his fretted electric instruments to play rock lines ala rock guitar.

It depends on the style, the player and the approach to music.

Frank