When most people think about exercise and losing weight, they automatically picture running, biking or swimming - a high intensity workout that burns a large amount of calories. They focus all their effort on cardio and completely ignore any of the benefits a strength training routine has to offer. They think more muscles = more weight, but this couldn't be further from what actually happens with a strength training routine.
The reason that most people don't want to put on muscle is because they are afraid of weight gain. Since muscle is more dense than fat, an area that was once taken up by fat will weigh more if you replace it with muscle. However, replacing fat with muscle isn't a simultaneous process.
Muscle Growth is Limited
You can lose about 2 pounds of fat per week through diet and exercise. That means you'll lose 8 pounds per month and 96 pounds per year. Muscle cannot grow at that pace. You'll be lucky if you can put on 10 pounds of muscle in an entire year, and that's if you're trying to gain weight by eating everything in your sight. Since you're on a calorie restricted diet, there's no way to gain enough muscle to offset the amount of fat you can lose.
The biggest benefit of strength training is that it allows you to keep muscle mass while losing weight. When you're on a weight loss plan, an unintended side affect is that you'll lose muscle. Why is it so important that you keep what muscle you have? Muscle, unlike fat, is metabolically active.
When you're sitting around watching TV or on the computer, fat tissue burns an insignificant amount of energy. Muscle tissue burns energy even when you aren't moving. This results in a speedier metabolism throughout the day which will help you burn more calories and lose weight faster. If you sit back and let yourself lose a lot of muscle, your metabolism will slow down which will affect how quickly you can lose weight.
When you're trying to lose weight, you need to combine cardio with strength training. Cardio will work to burn your body fat stores giving you a slimmer look while strength training will help build some muscle which will give you a toned look. If you only do cardio, you'll get skinny but you won't really have an athletic body. If you only do strength training, you might never get rid of the layer of fat that is covering your muscles. You can't have one without the other.
The Bottom Line
A well balanced exercise routine combines aspects of both cardio and strength training. You don't have to do them both everyday - cardio can be done 3-5 times per week while strength training can be done as little as 2-3 times per week for beginners. As you can see, you'll be doing a different workout everyday which will keep you from getting bored and get you more excited about working out.