Neighbor is a vice principal at a very high-achieving HS - had one student apply to over 40 colleges. Based on this kid’s personality, it was very ego-driven. He probably got into most or all since he was a high achiever, but I have no idea the mix of schools in terms of safety/match/reach.
We let D drive the college application process. She came up with the list of schools - 10 total - and we asked her what her thought process was in applying to them. A mix of UC’s (1 app, letters of rec for Berkeley), a Cal state (1 app), and some privates (Common App). Acceptances = 6, wait list = 1 (reach), rejections = 3 (reaches). Going to Berkeley.
Except for the exceptions noted by other posters, I cannot imagine needing to cast a net wider than 10 schools.