I sometimes have problems with getting a character's pose just right, and using 3D models (that I modeled and rigged myself) has been a huge help.
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(Chan-chan, drawn for r/moemorphism)
This process works full circle for me: draw a reference sketch → use it to create a 3D model → use the poseable model as a reference for future illustrations. More recently, I'm revisiting an older art style with different body proportions, and I've gone back to Blender to modify one of my existing models based on the sketches.
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Besides being a reference for 2D illustrations, I could also work on the base model even further and create a full 3D character (hair, clothing, etc.).