These days…very little. In recent years, 80-90% of all legacy applicants have been denied. Way too many apply, and they just cannot accept any more. Many are offered a streamlined path to transfer in later though. Of course… being related to an alum and also having them work there may help more than just being a traditional legacy.
For those looking to get “Chanced”, I suggest reading an excellent thread on the topic from the beginning…
I also suggest reading through the following very helpful insider’s guide to USC admissions. It directly discusses the legacy applicant scenario…
https://tfm.usc.edu/a-guide-to-uscs-college-admissions-process/
Best wishes… and Fight On!