"Tips" are the result of the fact that the "one slot" plan is not mathematically possible at the schools with the highest number of applicants. At these schools, where only 15% (or fewer) of the applicant pool are accepted, only one recruit in 7 would gain admission without tips. In that case the coach would have to entice 42 specs to apply in order to get 6 players admitted in each class! Not possible. That's were the A/B/C system and tipping comes from.
As Fenway mentioned, some of the schools also throw in the AI to match the IVY logic in order to use some math to counter the subjectivity. Regardless, the math of admissions makes a subjective advantage go to athletes in order for schools to field competitive teams and maintain long held athletic traditions.
CD is correct in that different administrations set different athletic priorities. At my son's school a new president decided a few years ago that the school's long history of athletics (one of the first schools in the country to have a baseball team) required more of a commitment from admissions. The baseball team got good very quickly after that!
The flip side of this is that the non-athlete has a decided disadvantage in that 10% of the class is athletic tips. This creates an ongoing debate on these campuses where some students resent tips, while tipped athletes point to debaters, musicians, etc. as equally advantaged as the tipped athlete. (intellectual kids argue about everything)
The math is clear, at the academic D3's an admissions preference is required for a baseball team to be competitive.