Check this out too. Mr. Larsen articulated in a much clearer way the way I saw this film than I ever could.
www.larsenonfilm.com/frank

Can I just say, I enjoyed every second of this movie. It's a pure joy to watch.

Lenny Abrahamson's Frank is one of those films where the film itself reflects what is happening in the film.

We see this character Frank as enigmatic, kind of a lowkey genius. The band members revere him, and Clara and the other band members are angered when newcomer Jon dares to challenge the status quo of the Frank's method.

Minor Spoilers Ahead:

We are to the film as the band is to Frank. You will know what I mean when you watch it.

The film is about the bravado of celebrity, the meaning of creativity, and the act we all put on for an idea, an image, and a status. In Frank's case, he felt that he had to maintain his image of eccentricity. The band had to remain different from any other band playing. The head had to stay on, because without it they just wouldn't be the same. Or, would they?

The band achieves a mythical status. Videos emerge on youtube of the band members having nervous breakdowns, and of this mysterious man dancing weirdly with a giant head on. Pay attention to the final performance of the band. Does it seem somehow different? Has it lost its mythical status? And is that a good thing? Regardless, it's a thing.

Once the head is finally removed, we are able to see Frank as a person with a beautiful slice of his own life to contribute creatively. The mask is gone. There was a time when the idea that Frank didn't care about what people think of him went so far that they began to pander just to keep that status. With the mask off, it's now honest. It's now human.