Some times when i'm shooting for groups I hold off the edge of the bulls eye so i can have a "finer" aiming point to go back to shot after shot, especially with a reticle or dots that cover up lots of the bulls eye. This helps me stay out of my head if the groups aren't being consistent. That way once I am done developing loads either factory from lot to lot or my own hand loads I get better feed back what the load is doing rather than me not holding center bulls eye for each shot.