Updated: Aug 29, 2019
If you think you ALWAYS trim corners as you sew...that is WRONG! I learned this all-important and reasonable rule from Claire Schaeffer way back in 2003 when I had her as the last guest teacher of my retail storefront days. Watch and understand:
Clarification of Trimming, Notching, Grading & Clipping
If clipping, trimming, grading, notching seam allowances and corners further mystifies you - be sure to watch this FULL video about it all. I've done my best to make sense of this 'engineering' with fabric.
One thing I'll add to the video above is: if you are notching a very lightweight, sheer fabric, and/or you are notching a very heavy fabric, you should stagger the notching, doing just 1 layer of the seam allowance, then move to the other layer just a bit next door, then back to the first seam allowance....this will accomplish the same thing, but will distribute the notching to yield a more uniform depth to the seam allowance.
Have these tasks challenged you in the past? Did this help? Do you have any tricks you want to share? Please comment below.