Answer:
The genetic material, DNA, is naked in prokaryotes. it is not complexed with any packaging protein.
Chromatin is strictly used for eukaryotic DNA, which is complexed with histone proteins. Thus, unlike prokaryotes, eukaryotes have their genetic material packaged tightly with the help of histone proteins. This packaging serves to compact DNA, so that 2 meter long DNA can fit inside a micrometer dimension of cell. At the same time eukaryotes need to transcribe DNA for which it should be made accessible. ATP-dependent remodelers help to unwound DNA. Specific acetylation and methylation of histone proteins also help to transcribe chromatin.
Thus, eukaryotic genetic material chromatin, is very complex in structure and cells have evolved over million of years to compact DNA, maintain and transcribe the chromatin structure.