A lot of the later demo effects on the c64 is using so called "speedcode" which basically is code generating code on the fly to achieve things like dynamically copying data areas. In effect intelligent loop unrolling i asm.
Anything you could do to minimise the amount of things needed to store, and their size, wasn't wasted time.
And though it might very ocassionally be similarly necessary on some chips today, it's more likely you'll work in assembly on those.