What does a pencil have over a mechanical pencil? Mechanical pencils never need sharpening, infinite supply of lead of various type and and they seem more environmentally friendly (assuming you keep using the same for many years).
You assume that drawing is 'all fine line', it is not. People who draw with pencils often use the 'side' to create feathered areas.
In my experience, mechanical pencil tips broke too easily. I've had cheap wooden pencils where it felt that the let was shattered inside which meant the sharpened tip kept falling out. That's how I felt about pretty much every mechanical pencil.