The patients benefit from the treatment significantly since a lot of time people who are manic are living recklessly, spending all their money, gambling, being hypersexual, trying drugs, getting into fights, committing crimes, tearing up their relationships, and the list goes on. The percent of people with bipolar disorder who die by suicide is 10-15%.
Patients who are hypomanic by definition aren't having marked impairments in social or occupational functioning and won't need to be hospitalized. There's nothing forcing someone who isn't currently on a psychiatric hold to take medication, so if they're taking it it's likely because they believe they're benefitting from it.