Im imagining that messi's late movement when hes without the ball is some kind of strategy the team has.
With the caliber player that he is, its no wonder that some club prefer man marking him. But when you mark a player that stay still or move slowly, you become doubtful. When the marker leaves him, thats when he find position. Proof: he still scored load of goals (which of course, some of them are also part of his mind work). One cant score so many goals when he isnt in the right place to receive passes from team mates.
Also this way, he conserve energy to burst it out during certain moment.
If this was the truth, then its not that hes lazy but its part of strategy. Just my two cents.