Why do you copy instead of subclass?

>when creating new form, I usually copy from existing form, and now I have this
>situation: in the DataEnvironment, I added some tables, but when I checked at the DE property, I saw lots of cursors/tables from the previous form. I have moved around the DE form and can't find those tables, but they do list in the property.
>
>1) how can I remove them?
>2) is there any harm if I leave it like that (in case I can't remove them)
>
>please advise
>thanks for the help.
>
>regards,
>
>Jerry