If you play on relaxed you will use less energy so if it is never reset, you can dominate later in the season.
It was tongue in cheek over the "effort" settings under tactics. If you don't recall the early days, you didn't reset to 100 every night. If you were gassed one game, your training was tied to how much energy you recouped between games.
Once everyone started playing for endgame, the process became outdated as no one cared about ehir energy at the younger days. They wanted the better long term training.