I talk a lot about thematic resonance — the idea that all of the parts of a transmedia work should feel fundamentally the same in mood and tone, if not in content. If your project is a moody, serious documentary about the aftermath of a natural disaster (just for example) then adding in a cheerful web comic with an animal mascot teaching you safety and survival tips probably isn't the best approach.
Thematic resonance is crucial. It serves to tie the pieces of your project together, to make everything feel connected. If the different elements of your work are substantially different in feeling, then the final result is going to be jarring to the audience. And it might actively work against whatever you're trying to accomplish.
The best way to illustrate this is the video for Wrecking Ball, by Miley Cyrus. Yes, I'm serious. Take a look.
Let's engage with this on a serious artistic level, all right? There's a lot going on here. On the level of lyrics and vocal performance, this is a powerful song about heartbreak. But the impact of the song is dampened by the performer's need or desire to appear sexual in the video. On the shallowest layer, it still works — the metaphor of the sledgehammer and wrecking ball destroying a relationship is a little heavy-handed, but that's fine. Lying in the ruins of the thing you destroyed? Great imagery.
But then there's the part with the licking a sledgehammer while making eyes at the camera. The nudity could still work; there could be a metaphor there about underlying vulnerability, but it's diminished or eliminated by the, well, the writhing.
Now, I have nothing against anyone in general or Miley in specific being sexy. I'm not engaging in moral panic here. If Miley wants to be sexy, more power to her; she's an adult now. But on the level of art, the sexy stuff dilutes this specific work on an artistic level, because this song and metaphor are fundamentally not about seduction. This results in a mixed message, with Miley singing tearfully about regret and sorrow, and then behaving visually in ways that would imply she enjoys and desires that kind of destruction.
There is no thematic resonance between the song itself and the visual performance. The pieces simply don't fit together as if they are parts of the same work, or the opinions of the same person, and as a result, the final video is much weaker on the level of art than it should have been.
By way of comparison, Robin Skouteris has done a mashup of Wrecking Ball and Sinead O'Connor's Nothing Compares 2 U.
Even ignoring the changes in the music and the addition of Sinead — this version works visually much better than the official Wrecking Ball video does, because it focuses sharply on the raw feeling of loss and despair. You know, what the song is actually about. You're not distracted from the emotion by thematic dissonance.
And this, kids, is why thematic resonance is important. Every detail of everything you make for a single project has to support the same emotional payload. Doing otherwise makes for worse art.