It is the natural thing to leave a plant to 'grow' but cabbages and cauliflowers once they get to a certain stage do burst out of that rounded form what ever size they get to.
Those wonderful uniform sized vegetables we see in the shops are a set standard. Some EEC ruling means that decent vegetables are thrown away, used for pig food or what ever because they are too big too small or wonky shaped.
When you grow your own you eat the lot. Part of the fun of it.