Healthy roots at the end of "rotting" ones

[Roberta]

Another reason for leaving roots even if they just have the core, is that when you repot, stability of the plant is vital for new roots to grow. If the plant wobbles, those new growing root tips get damaged and they stop growing. A bad root may still have the ability to hydrate the plant, but in addition it's a "handle" to hole the plant in place while it grows new ones.