I've been a workaholic. Sometimes it was great and I got tons of stuff done. Other times, I burned out.
Lots of people say, "Don't be a workaholic! You must have balance in your life!" Sorry, but sounds like a mere opinion to me. Everyone has a different idea of what balance means.
If you could work day and night, why not do it? The practical reason is that it's just not sustainable. Burnout is inevitable. (Maybe there's someone superhuman out there. But I don't know anyone personally. Paul Erdos?)
Still, this is a practical reason. I've never come up with a good philosophical reason not be a workaholic. Now, I think I have one. If you're a workaholic, it means you value your work above all other human endeavors. You might think of a priority system where you determine your priorities by how many hours you assign to each aspect of your life. When you're a workaholic, you've assigned infinite hours to your work; no finite number is good enough. In other words, you consider your work to be infinitely more important than anything else. This is a terrible mindset to have. Because there are many other interesting and worthy activities going on in the world. There are other important/brilliant people out there.
We've all met zealots who seem to think they are the most important people in the world. Don't become like that.