>>1239397Most steam locos did unless they wanted to crawl at 3mph up any sort of large grade. Modern trains go so fast in part because diesel-electric locos are so much lighter yet have greater pulling power.
Also even in situations where helpers weren't needed, they were used to help prevent speeding and assist braking since huge locomotives are large investments and large investments don't make money if they run out of control and derail. Even on flat ground, having brakes fail would represent a huge loss.
