What is the evolutionary advantage of introns in dna?

I understand what an intron is, but I don't actually understand what the point is of a dna sequence containing them. Why even bother wasting the time and energy to transcribe such a thing if it's not going to be used? How could this even confer an advantage to the cell?What is the evolutionary advantage of introns in dna?
More protein diversity. There are only about 23 000 genes in the human genome, but we make more than 2 million proteins. One of the ways this occurs is by alternative splicing of genes depending on which cell type you are.



For example, Cell 1 might use exons 1, 2, 3, 5, and 6 in making a protein, while Cell 2 might transcribe exons 2, 3, 4, 5, and 6 instead. This uses one gene, but makes two different proteins.