Safe, Balanced and Tight are three fixed confidence levels - 99%, 90% and 75% respectively - not three different ways of estimating the same thing.
Safe (99%) leaves the most buffer, at roughly a 1% chance of a stressful rush. Balanced (90%) is a good default, at roughly 10%. Tight (75%) cuts it closer, at roughly 25%.
Safe means more time spent at the airport on every single trip, most of which won't need it. Tight is a reasonable choice for a short, cheap-to-miss domestic hop; Safe makes more sense for an expensive once-a-year international trip with a tight connection.
These are general, statistically-modelled estimates - not a guarantee. Always allow extra time for anything unusual, and check your airline's and airport's own current guidance.