i tend to ALWAYS make a practice block when ever i am trying out a new block pattern so i can see just how it goes together and if i need scant seams or not...that way i can cut a little bigger if needed, or adjust my seams;
before jumping into a whole quilt. doing the practice block really answeres lots of questions, and lets you decide.
if you cut out your whole quilt in the beginning you are kind of commited...if you make a practice block you can change what ever you want to make it work for you. ;-)