One of the reasons for a T-tail or semi-T-tail (Caravelle, Falcon) on airliners and bizjets is the placement of the engines, which in turn is a result of the consideration that the plane has to operate from less-than ideal runways, keeping the engines clear from rocks, sand and/or wildlife they might ingest on takeoff.
Another one might be to keep the wings aerodynamically clean, making them more efficient and their construction lighter and easier to build.
These days, engines in pods under the wings are the preferred configuration as it makes them easier to maintain, and the behavior of such a configuration in the air is considered to be the safest and most predictable, also for other reasons besides the possibility of a deep/superstall
T-tails on high-wing jet aircraft (BAe-146, IL-76) are a different matter altogether though
