What are the advantages and disadvantages of fossil record in studying evolution?

The fossil record is skewed in favour of marine or freshwater organisms because those are the most likely environments to preserve signs of lifeforms.

Even animals living on land are mostly found as fossils in water-lain sediments after they were swept into water. That is why fossils of humans are very rare, if we lived in the sea there would be many more to find.

Also, the chances of any animal or plant being fossilised is very, very rare, even in the sea.