Not something most people would ever do at any point. Common use was the dried roots turned into powder.
Animals would be the ones nibbling on the fresh leaves.
The plant is strongest in the spring as it first comes up and people that have ever taken drugs or otherwise harmed their liver health, the caution is to not eat the fresh roots or leaves and instead dry them, powder them, etc…
best info on comfrey comes from the old dr. christopher videos