No, music is not a filler in a film. Yes, You are supposed to hear it. Music is supposed to invoke an emotional response to your scene. But you can't have music that is blatantly distracting. I'll walk you the first few steps to finding the right music.
The first thing I do is establish what's the mood of my scene. Then I establish what's the sound that's occurring in my scene. You don't want the music to be too dynamic if the scene is just a conversation. But if the music is driving the scene, then pick something that SETS the tone, and something that's MEMORABLE. The first resource I go to is FreeMusicArchive.org , a website where all the music is under public domain. They have genres for their genres, so I'd definitely check them out. If I can't find anything, I go on SoundCloud.com or BandCamp.com and look around for the artist that are killing it. Lemme show some of the go-to artists with their links a few embeds. If you can't view the embeds, then go here to view the article in safari. Scroll down past the artist to read more on choosing the right music.
*Try talking to the artist before using their music.*
Petualang // Soundtrack
Petualang is the go-to artist for soundtrack music. His music uses synths and xylophone-like rings like no other. In other words, his arpeggios drive the sound of his music.
Pax // Underground hip hop & chill beats
Pax has a diverse range of sound. Yet all of his music was made to be groovy one way or another.
Tomppabeats // (super) chill beats
Tomppabeats has music that is extremely emotional. His one-minute songs are super dope because their simplicity doesn't match how compelling they are.
David Chief // Euphoric electronic
David Chief is a great choice for electronic music that's euphoric. It's a genre that's really hard to find and he does it really well.
Andrew Applepie // (the Neistat music) all things electronic beats
Andrew Applepie is the majority of the music you hear in Casey Neistat vlogs. If you know Casey, you know that his music works great with his amazing drone shots. The big positive about Andrew Applepie is that he has a lot of music.
Back to the article
Whether you listened to every artist or you skipped all of them, let's finish the article. So there's a bunch of resources for good music in a film, now what. Well, what did you accomplish by looking for music? Is your scene going to be better in any way? Is your film going to be sound better? What's the point? If you answered no/nothing, then it may be best to revise your scene so that you can a music has a purpose. The soundtrack in a film often goes unappreciated. Music does what the camera can't. Don't undermine it, add music! If you wanna know how to add music (correctly), just keyframe it and loop it. Make the important parts louder than the less important parts. And if you like only one part of the song, then loop it (discretely). Most importantly, make sure you can always hear the dialogue. That's all you have to know on editing, but if you want a detailed version, check out this tutorial. Happy Shooting!