Of course, making sure that a “safety” school really is a safety is among the most important parts of making the application list. This time of year brings out posts about students being rejected or waitlisted from their “safeties” (or sometimes not getting enough financial aid and scholarships to make them affordable), which means that they were not really safeties.
Note that an understated wrinkle in assessing chances is that many schools have different admission buckets (other than well known “hook” categories like recruited athletes). A common type of admission bucketing is by major or division (e.g. applying to a popular division like engineering or business or a popular major like nursing may result in facing a significantly higher selection bar than most students). Admission bucketing may also be based on residency (commonly for public schools, though some private schools may look for geographic diversity). Some schools have automatic admission criteria which can make them admission safeties for students who qualify, but which are much more difficult to gain admission to otherwise (e.g. UT Austin).