Demo writers went to great lengths to get every last ounce of performance out of their target machine. Where games/application writers were concerned with stability/functionality of their software the demo writer was typically interested in how many CPU cycles routines would consume and how best to squeeze as much activity on the screen as possible.
Most demo's were written by "crews" with interesting names (e.g."The Care Bears", "The Lost Boys) usually devised of at least a coder and a graphics man and a musician.