What are resin fossils and why are they important?
Resin fossils were originally trapped in the resin (not saps) that some trees (especially needle-wood) exude.
We are talking mostly about small animals, like insects.
Once trapped, the resin conserves the insect, and when the resin itself gets fossilised into amber, the insect stays whole.
This way we can study every aspect of the insect -- there is no decay.
So, even microscopically, everything is still intact. You can't say that of fossils found in a stony environment.