Imagine the following situation: you have a list (possibly even an extended one) of records and you locate the record you want to edit. Next to the view window you have a form that would be suited to this task but you don't want to click on 'next' 137 times to get to the record you need to edit.
The solution is to bind the two windows together.
Settings Windows binding... will allow you to do just that: select the view that will be the source of changes (ie that would be the list in our example) in the combo box then select the form view in the list below.
Voila, it's working.
Note: There might be questionable behaviour when this case happens: you have two forms linked together and edit both of them; you then click next on one.
Which form is saved ?
The one where you clicked next. Changes made to the other one will be lost and there won't be any warnings.