Strength training helps build and maintain lean muscle mass. Muscle tissue requires more energy (calories) to maintain than fat tissue. The more muscle you have, the higher your resting metabolic rate, meaning you burn more calories even when you're at rest.
During a strength training workout, you burn calories not only while exercising but also during the recovery period as your body repairs and rebuilds muscle. This effect is known as excess post-exercise oxygen consumption (EPOC) or the "afterburn."
While the number on the scale may not change significantly (or may even increase slightly) when you start strength training due to muscle gain, you will notice positive changes in your body composition.
Strength training helps you lose fat, especially when combined with a calorie-controlled diet. It reduces visceral fat, the fat stored deep within the abdominal cavity, which is associated with a higher risk of health issues.
Building muscle through strength training can boost your metabolism, which is beneficial for long-term weight management. A faster metabolism helps you maintain your weight loss and makes it easier to manage your calorie intake.