Feel free to use these to "scroll" through results instead of having to generate the correct URLs. Hopefully this will make API clients a bit simpler to write and maintain. There are various tools depending on your programming language of choice which will make it very easy to use these. Here's an example of a popular Python HTTP client library's handling of these headers: http://docs.python-requests.org/en/master/user/advanced/#link-headers .
2. Total results count:
We have gone for an API with an envelope (metadata + results contained in the body of the response). Thus, you already have access to this information in the "total" key in the Discovery API responses. However, this header is used by a number of other API-s, so we're providing it for convenience and for those who are used to having it.