When raising young children, you don’t get to keep all your energy. You need to give a lot of it to your child and the day-to-day activities associated with raising them. You do, of course, have some energy left over which you use to keep the rest of your life running: work, relationships, friends, hobbies, etc. My highly unscientific estimate is that you have around 70% of your normal energy left (much less for newborns).
Strictly by the numbers this should be a detriment, with less energy for work, less for friends. The strange thing I’ve noticed is that I actually function better on 70% energy than on 100% . I’m not sure the exact reason but I think focus and perspective are the main culprits.
With only 70% energy to work with in a given day, the amount of bullshit I put up with is almost zero. Since having a kid a year and a half ago, the amount of meaningful things I get done has gone up. The amount of TV I watch has gone down. The number of grudges I hold and times I get offended has gone down. It all adds up to a more efficient and satisfying use of energy.
Here’s to operating at 70%!
 I’ve noticed this when I play soccer as well: I play better after burning off around 30% of my excess energy. It calms me down and forces me to play smarter.