I always tell people who reach out to me that preparation is key. Knowing your blind spots and getting unfiltered feedback helps you as a candidate to get the best offer and your most desired employer. Candidates who do mock interviews get multiple offers from companies and that puts them in the drivers seat to decide which employer or team they would like to join.
Another side effect that most people do not realize is that the seniority and the pay you get offered even when you do well at an interview depends on how well you do at an interview. If you get an 7 on 10 thats good but if you get a 9 on 10 then you get a better level and are in a totally different pay band.