Hemming/Shortening Pants and/or Slacks
If the legs are tapered/narrowed towards the bottom and I need to shorten them - I like to pin them first to see if I need to open the inseam or outside seam so that there won't be a "gather/pucker" where the hem is stitched down.
When the legs are tapered, the part towards the foot is narrower than the part towards the waist - so I have to get some more fabric on the narrow part - so I "steal" it from the seam allowances.