Well, I'm a drummer. I've been drumming for the past three years. I can read sheet music and I had this question. What's the point of having 'rests' in drums. I mean, why can't you leave the part where you want a rest, blank?
It's easy to think that a short sound just needs a blob on the music, but it's easier to count through the bars if each one has the prescribed number of beats. Imagine a snare on 2 and 4. If the rests on 1 and 3 weren't marked, you may well think that the first snare hit was on 1. Who knows?
Whilst most drum sounds are short, cymbals can ring for a whole bar at least. If the composer wanted a short cymbal sound, a quaver (really short), crotchet,(longer) with appropriate rests to say 'stop it now' gives great information.
The rest signs are exactly what they say - no noise now, for this long.
Imagine a rest as a placeholder signifying the presence of nothing, sort of like how 0 acts in mathematics. While not actually anything, it relays the information that there is literally nothing there. You could imagine how impossible it would be to decipher a number with no placeholders for nothing.
So instead of an action looking like this, with 1 being a note and 0 being a rest, or empty space:
This hemiola depends on understanding the space between sound. Without rest as placeholders for silence, you would get something that looks like this:
1 | 1 | 1 | 1|
Whoops, that doesn't make sense anymore. It looks like you're trying to guess where the beat is.
In the end, it's all for greater precision and accuracy, especially when playing with others.