Prokaryotes does not have introns as here transcription process is coupled to translation. Neither they have time nor space for the separation of process. If intron splicing would have occurred then it would have stopped the coupling which is not possible in the prokaryotes. Also they don’t have specialized nucleus like eukaryotes. In eukaryotes splicing of introns occur in nucleus.
Eukaryotic cells are more complex than prokaryotic ones and also these have to splice their introns before translation which require more energy input than the simple prokaryotes which don’t have introns.
Eukaryotes have a greater opportunity to control gene expression as eukaryotes have a complex lay out of many genes and lot of junk DNA which helps in the regulation of gene. Prokaryotes on the other hand have lesser genes and thus the control of gene regulation is not very accrate.