Both types of training are required for general health maintenance, as well as to lose weight. Think of it this way, strength training adds lean muscle. Lean muscle burns more fat during rest – thus increasing your basal (resting) metabolic rate. This increase in basal metabolic rate can positively offset the decrease in basal metabolic rate that dieters often see once their body goes into ‘save everything mode.’ It’s a good way to keep your metabolism up, while slimming calories from your daily intake.
Cardio exercise (if in the aerobic, or fat burning, state) is known to burn calories from fat. This is a great way to create a caloric deficit, & combined with some caloric reduction in terms of what you eat, will create the total caloric deficit you need to steadily lose weight.
Not to mention the vast health benefits of a balance exercise routine that includes both resistance (strength) training & cardiovascular training – good for bone health, heart health, and as a way of preventing the onset of some major illness. You’ll sleep better, feel better, and look better, too!
Good luck in your training.