Is it a crop you sowed last year and have overwintered in the ground?
If so, they will be on the move to shoot up and flower as soon as they can. I would take a couple crops of leaves at the most, then dig the roots up. I think it is only the very young leaves that are palatable. If you use older leaves is it only the bottom end that is eaten, but letting them grow tall is of no benefit to you as it will sap the root.
The flowers are very pretty and bees love them.