Pellet size/shape is mainly related to the flowability and melting capacity at the screw. Commonly there is a range of such properties given an specific extruder/injection machine.

It depends on the application. In optical application nano size of the particle might be important. In industry if you have for example porous resins for ion exchange applications they should be big, otherwise you will have very high "Pressure Drop" through your flow system. That;s usually what the pellet is about in industry, pressure drop.

Thank for for your reply. Can any one shine light on importance of these in plastic industry (while processing, etc.)?

Pellet size/shape is mainly related to the flowability and melting capacity at the screw. Commonly there is a range of such properties given an specific extruder/injection machine.