I find conventional Western notation works quite well for communicating notes, rhythms, and basic expression, but it breaks down pretty quickly once you move beyond that. E.g. a lot of the common techniques on electric guitar (bends, palm muting, tremolo/whammy bar stuff, pick slides, slap/thumping, pinch harmonics, raking) don't really have a convenient notational shorthand. That's without even mentioning synthesizers (how do you notate 'gradually increase the filter cutoff here'?) and DAWs, samplers, drum machines. But it's definitely a hard problem: the more information you try to shove into a notational system, the harder it gets for people to keep track of what everything means. Plus you just start running out of easily distinguishable symbols at some point.