Internal friction due to stuffing materials. - Why does it not matter? If it does then there must be some limits like rpm etc.
Not entirely leak proof. - Why are we supposed to keep it leaking (installation)
Have o-rings eliminated stuffing boxes?
Edit: Stuffing box is a dynamic sealing mechanism --like o rings (static and dynamic sealing). They are used as seals in rotating, translating mechanisms.
To better understand here are 2 examples.
- Steam engines: if there was no stuffing box, all the steam would leak out of the piston rod side-- not creating pressure. In petrol/diesel engines, SB is replaced by piston rings. From SB in Steam Engine
- Boats: if there was no SB, water will start filling the boat from the hole -used for the propeller shaft. From Stuffing Box: