Well, there is a technical answer—being that drums as unpitched rhythm instruments are obviously there to keep time, they basically do the “same” thing as a conductor or a metronome—but the “technical” answer—as so often in art—is also the least helpful.
The role of drums can span literally from “there are no drums, ergo no role” to “being the entirety of the music in question”, depending on genre or even just musical piece in question.
Most often, the drums—together with the bass—are meant to be the rhythmic backbone of a track. They not only keep the time, they also play on or against the beat—usually both, changing depending on context, rarely are the drums only on beat or only off-beat—creating a “skeleton” of pulses and rhythmic accents that help in understanding—or, when deliberately misdirecting, help confuse about—the other instruments, putting them in a rhythmic—and, together with the bass, a harmonic—context. It can be jarringly surprising how much the subjective feel of a melody or harmony changes if you just change the beat around it, even if you don’t put it in a different time.
Of course, there are exceptions and additions to this extremely wide field of what drums are supposed to do—for example, a blastbeat is very much not about actual rhythm as it is about sheer sonic violence, the speed and intensity just serving to make everything else seem more intense as well, and on a wider note, intensity (or lack thereof) is another thing drums are pretty much always a crucial part of—but, let’s be real: if you were to try to write down each and every of those, it not only would it become a novel of epic length, it also would never actually incorporate everything people can come up with… and honestly, this is probably true for every instrument ever conceived.
So, yeah, on the most basic level and in the most casual of lazy explanations, the drums are usually a better metronome—which says, of course, just about nothing about the actual impact of the drums on a musical piece.[from https://ift.tt/1n4oEI8]