A level 7 doctor will reduce the length of injury suffered (at the time the injury is suffered) by more than a level 1 doctor. So with a level 7 doctor, you will have fewer 5 week injuries and more only until game end injuries. A level 7 doctor with taping will have the same chance to allow an end-of-game injury to return in the middle of the game as a level 1 doctor with taping will.
A level 7 trainer will train more effectively than a level 1 trainer (you get pops faster). A level 7 trainer with Career Extension will get the same reduction in the rate of skill loss for old players as a level 1 trainer with Career Extension.
A level 7 PR manager will improve your merchandise sales and attendance more than a level 1 PR manager. A level 7 PR manager with Crowd Involvement will increase your home court advantage effects the same as a level 1 PR manager with Crowd Involvement.