[quote name='Aguycalledphil' timestamp='1422227118' post='2670196']
Is it vital to be able to master one finger per fret?
[/quote]
In a word, no!
Depends where you are playing on the neck. If you are playing further up towards the body end then it will be easier to play one finger one fret. Playing nearer the nut it will be more difficult, so use the 1,2,4 fingering over three frets. Dave Marks has something to say about it in the clip below.
http://youtu.be/eXkxu_7Tn48