Ah.. You do want to cut off the roots: once you re-plant, the old roots will rot. By cutting the roots you also encourage plants to grow new roots faster.
The rule of thumb: cut all roots to ~2" every time you re-plant. The rule does not apply to plants like Water Sprite, anubias, ferns.
Courtesy * Integrity * Perseverance * Indominable Spirit * and Self Control
Tenets of TKD