What are considered well accepted advantages of a mental health care plan?

Insurance likes it. Some policies expect to see a treatment plan if they are going to pay for your treatment. Moreover the treatment plan gets everyone involved in your therapy (including you!) in establishing specific goals and timeframes.
Formal benefits? Perhaps you mean "benefits" as the policy indicates, i.e., what conditions and treatments the policy pays for, and the limitations and exclusions. If so, these vary greatly from policy to policy and from state to state. You would be wise to check with an insurance agent, as these can be very complex. They are also in flux as the "patient protection and affordable care act" ("obamacare") begins.