In the design cycle, users can have multiple versions of projects which use the same IPs with the same configurations. Rerunning the whole project can cause regeneration of the IPs every time, and is time-consuming.
In the Vivado project settings, the user IP repositories allow users to add their own IP to the Vivado IP catalog and when used alongside a Remote IP Cache, compile times can significantly reduce. This blog entry explains how to set this up.
You can find all of the entries in the Saving Compile Time Series here.