You can only load one form (unless that form has its own subform) at a time in a navigation control. Switch tabs, one form closes, the other opens. That means any code associated with those actions will run, or at least any record changes will commit.
Not finished entering data on formA and you switch to formB? Too bad...
Want to get a value from formA when on formB? So sad...
Then there's the convoluted syntax for referring to anything on a form that's loaded into a nav control, and if that form has a subform it's even worse.
You can replicate the look of a nav form with a tab control and pages (why didn't they call it a page control?) and a set of side buttons that look pretty much the same. Do you need 7 pages for 7 forms that you might want to show? Not necessarily. You can change what loads into one page based on what side button you click. Or you can have 7 pages and only load a form when you click on it if you need your main form to load faster.
The only time I use a nav form is to try and help people who have issues with them, and there's plenty of those.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.