I would like to use GRCh38 as a reference sequence for NGS data analysis. I tried to get the file of GRCh38 at iGenomes. https://jp.support.illumina.com/sequencing/sequencing_software/igenome.html
At the site, I noticed that there is the link of decoy for only GRCh38 (GRCh38decoy). It seems that there is no link of decoy for hg38, hg19, GRCh37. Why is there the link for only GRCh38?
When I use the GRCh38 as a reference sequence for NGS data analysis, should I use GRCh38decoy? If I should use it, could you please tell me how to use it?