Pros of single model per file:

• Imported nodes contain only what's related to a specific single prefab
• Editor needs to re-import only what has changed, not the whole file

Cons of single model per file:

• Can't easily work with multiple models at the same time
• Can't compare model scale and alignment easily in Blender
• Can't reuse materials or textures easily
• Multiple Blender files will take more space than just a few