What is the key advantage of grouping genes of related function into one transcription unit?

Having genes with related function in one transcription unit is important because such transcription unit will have a single on and off switch. This switch can control expression of this group of genes in a more coordinated manner than when each gene has its own regulatory system. It ensures that these genes are transcribed together as a unit and therefore there functions are highly coordinated since they are related.    

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