I guess it depends on how you want to interact with them. If I had to continually mouse over and click on them in order to be able to relate data between them I think I'd find that tiresome. Also, if you're opening formB to add data that formA needs then IMO the subsequent form would have to be modal, and that won't work if more forms have to be opened to support the effort. An alternative might be a main form with subforms, but again, it depends on what you're doing with these forms.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.