I do understand micrometer observation. And i see that it supports adding lowCardinalityKeyValue and highCardinalityKeyValue with something like below –

Observation observation = Observation.start("my.operation", registry)
    .contextualName("span name")
    .lowCardinalityKeyValue("this.tag", "will end up as a meter tag and a span tag")
    .highCardinalityKeyValue("but.this.tag", "will end up as a span tag only");

I do understand what these KeyValues mean, but can some one give a real world use case where such distinguishing make more sense.