I took a class at the local quilt store where they taught both ways. Even with getting a perfect 1/4" seam allowance, I still had trouble getting a perfect half-square triangle block when I did the 7/8". But when I rounded up to the next inch (or half inch) and square up after wards, I had perfect blocks. The amount of wasted fabric is very small. And the extra time is well worth it especially since it's less stressful. And if you square up the small units as you piece along, the bigger block will go together and lay flat better.
Happy quilting.