Using the whole bow does create more power and volume as can using a shorter amount of bow from between the frog and the mid section, however the quality of sound can be quite different. You tend to get a much smoother and flowing volume by using the whole bow and a shorter amount of bow tends to be used for faster or more aggresive playing.
You can play fast fiddle tunes with the whole of the bow but a slurring tecnique is required in most cases and sometimes the movement and life of the music is lost.

One exercise I used to do is playing a tune and being able to deliver it with the same amount of accuracy and pressure wherever I held the bow from the tip to the frog, it can only be done with a relaxed hand and is good way to practice. I also practice cello style so I can play my fiddle in any position.

I am a classically trained violinist from the age of 3, who turned to folk music at 16 after hearing Ric Saunders on his One to One tour with Gordon Giltrap when I was 8.
My classical training has proved very usefull but my playing has certainly changed.

Only my opinions, works for some not for others.
Becks