Not always an issue. On one shed, with an outswing door, it has never been an issue in 25 years. On the shed with the inswing door, it would always have to be scooped out.If you are in snow country you will want the door to open in.
Then threshold. SorryWhat is your definition of a "sill plate"?
To me a "sill plate" is the pressure treated 2x joining the wall. A threshold is what comes on most exterior doors and is usually siliconed down.
