Hi Chris,
Dragonslayer is right on the money about using it as a vehicle to better learn the neck of the instrument. the ability to flow from one position to the next is an integral part in advancing on the fiddle or mandolin (or any instrument for that matter.
Fiddle tunes can have as much improvisation as any other music. They are the same as any break in the respect that there are certain melody target notes, but even those are up interpretation.
If you want examples, go listen to five champion fiddlers play the same fiddle tune. They may all hold the integrity of the tune but may accomplish it in completely different ways or from different positions on the neck…