This is a guy that doesn’t watch basketball outside of box scores.
It has nothing to do with conserving energy. Whiteside will switch onto a PF with three point range, watch him go to the corner to spot up, and still stay glued near the paint so he can try to grab a block or rebound. He does this by DEFAULT so great teams with good playmakers will exploit this.
He will chase blocks instead of playing good defense. I’ve seen Whiteside jump to get a block in situations where he doesn’t need to, just because the shot goes up, and it’ll turn into Easy offensive rebounds because he stopped boxing out a big to chase an entirely unneeded block.
He doesn’t know how to defend in space. He lacks lateral quickness and bad footwork outside the paint. When his man sets a screen, he refuses to show consistently and leaves the smaller guard (Dragic, Lillian’s, McCollum) stuck trying to fight over the screen which will allow for open threes. He always sinks to cut off the paint and will give up open mid-range shots over and over. He gets attacked like this so consistently that it makes hard to go on real runs with him in the game especially against good teams.
Whiteside doesn’t have a game that translates to playoff success.