As Lead why should you be looking anywhere else? The mechanics manual is written to put officials in the best position to officiate plays in their primary areas. Rebounding plays often start before any shot is taken....bodies are banging trying to secure better position. Why would you ever take your eyes off of that to officiate someone else's play? You need to identify the defenders, the small/big matchups, who is displacing who first, etc. and doing that requires focusing on the players in your area as Lead from the start of the action, during the development of the action, through the finishing of the play.