Answer
Metagenomic studies have allowed in-depth research on prokaryotes that could previously not be investigated due to our inability to keep them alive under lab conditions. Prior to this, the true scale of diversity among prokaryotes was unknown.
Molecular systematics have revealed an evolutionary history and diversity among prokaryotes that was previously not understood, the most dramatic being the differentiation of Archaea from Bacteria.
Work Step by Step
For metagenomics, consider that this approach specifically uses environmental specimens. Remember that we can only keep a tiny fraction of all prokaryotes alive in the lab. Were we limited to the study of only those organisms that could live within these narrow capabilities, our ability to research prokaryotes overall as a whole would be greatly limited.
Molecular systematic research revealed the division between Archaea and Bacteria, which is of course foundational to our understanding of prokaryote phylogeny.
