Going back to 2009 with Fedora 11 has been delta RPM support to enable support with Yum for these packages that just contain the differences between one installed RPM version to the next version. With Fedora frequently pushing down new packages, delta RPMs have allowed those in bandwidth-constrained environments to more easily download updates since the file sizes of the deltas tend to be significantly smaller than full RPMs. Additionally, it's placed less of a burden on the Fedora infrastructure by having less disk space and bandwidth requirements. However, with DNF it looks like Fedora could revert to going back to full RPMs for distribution of updates...
October 6, 2014
Fedora Might End Up Disabling Delta RPMs By Default
Read more at Phoronix