1. If it's in an attached garage, you can't work out at nap time.
2. Kids will want to watch you work out. (they can wonder in and get crushed by the weights)
3. Random stuff will migrate to the gym (you want dirty clothes hanging from the squat rack? You got it.)
4. The loss of focus being so close to home.
5. Phone call? Yeah, you have to answer that.
6. Crying kid can still be heard...Fuck you, nap time.