There are several significant drawbacks to being in a hypomanic state.

1. It's physically harmful. Sleeping six hours every three days is probably unhealthy by itself, but I sometimes push myself beyond my physical limits in other ways, and end up injuring myself.
2. It's psychologically dangerous. The longer I spend in a hypomanic state, the more likely it is that I will crash straight into severe depression. Unlike depression, hypomania regresses to the mean, and I've never had one last longer than two weeks. I suspect this is mostly physical exhaustion catching up to me.
3. It's short-sighted. In a hypomanic state, I act in an optimistic near-mode all the time. I don't plan for the future, I don't realistically assess risks, and I manage my time (including the new excess) very poorly.
4. It's not creative. While hypomanic, I don't think, I just do. I've never come up with a worthwhile research idea while in a hypomanic state, although I've occasionally thought I have. While I have a huge amount of energy to devote to projects, I'm much more likely to tackle the wrong project because it's the first one I thought of. I've heard people exhibit similar behaviors when using Adderall to boost mental performance.

I've heard discussions about the usefulness of alternate states for different kinds of work, and hypomania is useful when I have a specific thing that I am already doing and willing to keep doing, but is too tiring for me to expect to finish in time. I saw a study that indicated people (neurotypicals, without a history of depression) are better at critical thinking when (mildly) depressed. This may be the case for me, but depression is way too severe for me to consider using it as a tool; regardless, I can't coax my depressed self to do the simplest things, so I don't know where the motivation would come from.