Schools that want to protect their yield number may react negatively to excessive applications
Keep in mind that unless it is "leaked" to a school (i.e. by student, parents, guidance counsellor, teacher), the school does not know what other schools you have applied to. As per U.S. Anti-trust law, it is illegal for school admissions to be colluding with each other.
That said... even though it's illegal, it's a black box to me what actually goes on behind the scenes.