Debian blu-ray and dvd both have 3 disks, what is the purpose of the blu-ray discs?

I tried to download the Debian "testing" (aka "stretch) [install media that is blu-ray](http://cdimage.debian.org/cdimage/stretch_di_alpha5/amd64/jigdo-bd/) because I wanted a one disk solution. When I went to the Debian site to download the blu-ray disk... there was 3 disks... arg. The regular Debian dvd install media also has 3 disks. **Given that the dvd and blu-ray install media both have 3 disks... what is the purpose of the blu-ray version?** - [debian "testing" (aka "stretch") install media](https://www.debian.org/devel/debian-installer/) - [blu-ray media](http://cdimage.debian.org/cdimage/stretch_di_alpha5/amd64/jigdo-bd/) - [dvd media](http://cdimage.debian.org/cdimage/stretch_di_alpha5/amd64/iso-dvd/)