For a responsive site, what other resolution does the designer need to make 640 or 768?

Question

Adaptive design

For a responsive site, what other resolution does the designer need to make 640 or 768?
Our basic permissions have been approved and are being made: 320 and 1200
But a question arose with intermediate ones. Do 640 or 768?
Logically, it is convenient to break the design into 4 parts. Then like 640 is necessary. And the layout designer will pull out the intermediate ones.
While we plan to do: 320, 640, 1200.

Answer 1

Of course, the 768 is much more useful because it's the width of an iPad and a bunch of other tablets with similar screens. This is a really common and popular size.
And 640 is... Well, this is the horizontal size of some phones, but no one watches sites on the phone in landscape orientation.
mydevice.io/devices

Answer 2

These points are not the issue.
It is necessary to make a harmonious design at all points of 320-1200 p.
For this, it is necessary that the layout designer clearly understands how the elements, blocks of the site will be compressed at all resolutions.