Lots of use-cases for UKM would help with more knowledge of the entire redirect chain (not just the first + last URL). Still, even having the first URL would be helpful.

For instance, someone using a Safe Browsing type of block list that checks _every_ URL in the redirect chain may want to evaluate impact of launching a new URL to the block list. With UKM, you could simply write a query to establish the total % of UKM traffic with that site anywhere in the redirect chain.