The harder you train the better the results will be to a certain extent.
I say to an extent because one thing we must understand is that are muscles are not growing while we train but while we rest.
What we are actually doing when we lift weights is breaking down and tearing the muscle.
This breaking down of the muscle fibers is obviously a necessary step in muscle building but the muscles don't actually start rebuilding and growing until they are at rest and have a chance to do so.
Never under any circumstances, unless you enjoy wasting your time, should you train the same muscles on consecutive days.
For example, if you train chest and triceps on Monday try and stay away from using them in any lifts on Tuesday as they haven't had a chance to heal properly.
My personal routine right now (and it changes many times a year) is a full body weight training routine followed by a day of cardio followed by a day of rest.
This gives me two days off from breaking down my muscle fibers and I've seen the best gains using the 2 days off weight training method.
Different bodies will adapt differently and require different variances but all bodies need sufficient rest to grow and that cannot be overstated.
Overtraining can lead to serious injuries and then you won't be doing any weight training at all.
You should always try to get at least 8 hours of sleep (I have 3 kids and one of them is an 8 month old so I know this isn't always possible), keep your protein intake up and your fat intake in check to optimize your muscle growth while at rest.
Also, don't look at muscle soreness as the only sign to gauging whether or not your muscles are in need of rest.
Veteran lifters often feel very little to no soreness the day after a lifting session but they know pain or no pain the muscles are in a healing state and should not be disturbed.
Lastly, if you're a year-round weekend warrior like me you should consider taking a week off from time to time to let your muscles heal and central nervous system rebalance itself so to speak.
Your central nervous system takes a heavy beating during intense training and needs the same care as your muscles.
Good luck in your training! Train Better, Chad Hamilton