Do not close disc?

I have been using Ulead MovieFactory to convert some VHS stuff to DVD, using an ASUS drive. My question is about an option in the ‘burning options’ of MovieFactory. There is a field called ‘Do not close disc’ which I thought would leave the DVD disc open in order that more files could be added.
However whenever I try this it just tells me that the disc has already been used or if I use a RW disc it asks if I want to erase what is on it.

Is it possible to ‘add-on’ additional files and if so how do I do this?

Thanks in advance.

If you want to add more video footage to a disc using DVDMF, then it must be an RW disc and I think you need to use the ‘Edit Disc’ option right from the start.