Red Wizards aren’t known for being nice. They also aren’t known for a high survival rate among their apprentices. Since they ARE known for forcibly conscripting magically talented humans into their service, they are also known for a high ratio of scrawny, scared apprentices to powerful, tyrannical, and cruel master wizards. Since those same masters practice circle magic, having many bodies to feed them energy is helpful, and apprentices, while not exactly valued per say, are considered a useful resource.
Of course, one often has a surplus.
In these not uncommon situations, it was customary to assign the more senior apprentices (meaning the ones who had managed to survive everything else their Master inflicted, and who might not be completely harmless anymore) an impossible and suicidally dangerous task.
And sealing that with a geas.
This was always portrayed as a “graduation exercise”, but the Masters weren’t fooling anyone.
It was generally considered to be better than the alternative, though.