I’ve often said that one of the biggest concepts that drives most of the music you listen to is tension and release. If you have a band playing a simple groove on one chord, there isn’t much tension. But change up the rhythm or put in an interesting fill and you create a bit of tension for the listener that is released when you get back to the home-base groove.
These fills are a pretty common way of quickly creating and then releasing that tension with a note grouping that creates a bit of a polyrhythm. In Ex. 1 you can see that the second measure starts with a three—sixteenth-note phrase (cymbal/snare, bass, bass) that is repeated four times over three beats. That creates the tension with a four-over-three polyrhythm. Then you go right back to the beat and, ta-dah, no more tension. The rest of these examples are variations on that theme. These are powerful fills that can be used at the ends of phrases to help set up what’s coming next in your music.