Meditation will benefit you nevertheless, but if you start (as many people) to address some condition that already exists, addressing it first will help you to continue exploring other benefits. For example, when you suffer from depression, perhaps first you need to explore what causes this state. In major depressive disorder, the condition is caused by excess stress, which can come from any of your lifestyle areas.
To overcome depression and prevent its relapse, it is not as much as eliminating the source of your stress, but to change your understanding of the stressors and your approach to them. It won’t always be possible to block what stresses you, but it is possible to change the way you see it, so the same event won’t make your cortisol jump. When you know where the stress originates from, start approaching with mindfulness the way you interpret the stressor. It is not the event that makes you feel bad, it’s your interpretation of the event.