Everything has gone digital, irrespective of the fact that being a pencil artist is more inspirational and makes your art work more appeal to creative flux revealing subconscious ideas. You just have to have to follow the modern way of sketching.
If I’m not mistaken, I hope you mean the greatest weakness of sketching on the paper for a pencil artist cos my opinion boils down to the cons of sketching on paper as the weakness of a pencil artist.
The pros of using the digital equipment for sketching are the greatest disadvantage of being pencil artist.
Digital tools save time and space; it makes your work available one place and is essay to access. In addition, you get better result in a far shorter period of time instead of sketching on the paper.
The experience you get is far better than sketching on the paper; Here a pencil artist, keep losing his art work or drawing materials around the house, especially when you have pet like cat at home, or it can be accidentally destroyed by family. But using digital helps you arrange, save your sketches and makes some copies.
With digital tools, you can easily erase your mistakes, just by using the ‘Undo’ button, scan your work and share to friends which will help you attract potential employers.