The importance of using weights is crucial to strengthening the body. Although stress is considered undesirable, the stress you endure while lifting weights is good for you.
Weights are tricky because you first need to know your body and the amount of strain it can endure while lifting weights. Lifting too heavy or too light are counter productive for a workout program. You always want to have a gradual progression in weight and reps.
For certain lifts such as bench press, squats, and power cleans, good technique is required to be effective. Having a spotter nearby is very important for safety reasons, especially when you're first starting out using weights.
In addition, you don't always have to use weights to get a great workout and increase your strength. Here is what Tyler Graham at Men's Journal has to say about bodyweight workouts:
"The key to bodyweight exercise is mixing it up. Challenge yourself. If you're not sore the next day, you didn't work out hard enough. "When you push yourself, you'll be building muscle, increasing bone density, strengthening ligaments, and burning calories for up to 36 hours after your workout," says Mark Lauren, author of 'You Are Your Own Gym.' When push-ups become too easy, switch to a different grip - wide, narrow, or staggered hands - or pause during the motion. Try one set on an incline, the next on a decline, and the next with one hand on a basketball. For all of the exercises below, aim for three sets of 10 reps unless noted otherwise. Time yourself and try to do them more quickly the next time around. If you can't finish a set, complete it with the easier version."