Once you've adequately worn out your muscles during a weight training session, the tissues need time to rebuild/repair in order to thicken. It typically takes between 48-72 hours for that to happen.
Rest is also important so that you are able to maintain proper form at the next weight training session.
No point pushing hard and keeping the body at constant stress when lifting form is sacrificed. Remember, you are a body-builder, not a weight-lifter!
However, if you feel you want to maximise your time at the gym and workout everyday, you may want to consider slotting in cardio training on non-weight training days.
Monday- Day 1 Weight Training
Wednesday- Day 2 Weight Training
Friday- Day 3 Weight Training
The above is strictly for "normal" people who are into training for fitness purpose.
Professional body builders train up 3 times a day, 5 days a week. Now, that's a different matter all together...