I'm not sure if I am understanding you correctly but the following may answer your question.
If you omit the viewport meta tag then the device will try and scale the page to fit the device as best as it can.
If you add the viewport meta tag then its up to you to set the appropriate width for the device (via media queries). If you don't adapt the layout then it will stick out of the viewport as though you had just closed the window on a desktop machine and sized it down to 320px.
If you are talking about something else such as the values for initial-scale in the viewport meta tag then that is a different concept.
I'm not quite clear on which aspect you are querying but form your comments about 960px width then I guess you are finding that content on an ipad is sticking out of the viewport. If so then that's because you have added the viewport meta tag and the ipad expects you to adjust the layout to make it fit properly. If you remove the meta tag then the ipad will scale the page smaller to fit automatically (within reason).
The main point is that if you are building a responsive web site then you need the viewport meta tag so that the mobile device takes note of the media queries you are setting which will control how the layout looks.
If you have not build a responsive layout and don't use media queries then omit the viewport meta tag.