Actually it does. You have to use more energy to warm them up in order to properly train WITHOUT injury and get them back to a more reasonable weight. I don't know about you, HP, but I don't waste my money on super healing potions at all. I train completely without them. I prefer it that way. If I occasionally get an injury while training, that creatu gets a break for the day... which rarely happens.
Using more energy during warmup means you gain less stat points per day. I can get 2 stat points per creatu per day usually, though that can vary at times, depending on what I'm training. I don't train a creatu in just one stat at a time, I want them balanced according to their personality.
So, if I'm forced out of training for more than one day, my stat gains per day slow down. Don't like it, especially right now when I can finish the games and other dailies in less than half an hour.
And putting while putting creatu in the shop overnight to reset all stats, that's just not realistic. Not to mention, you loose all progress. I'd rather not have my creatu suddently blow up into balloons if I have to go on a weekend trip for class, and loose the 23/25 health points to gain another health point for my creatu.