Here is an example. Say you are testing an ebook reader web app. The app lets users highlight text, add notes to highlighted text, view all their highlights & notes in the book, search for specific text in the entire book and more.
There are two test cases to validate the highlighting & adding notes to a web page. One test simply picks any page from the table of contents and checks if you can do highlights and notes there. The other test searches a word, goes to any page containing that word and then checks if you can do highlights & notes there.
The question is do we really need both of the above tests to validate highlighting & notes ?
I believe that the first test is enough because the goal is to validate highlighting & notes on a web page, and not different ways to get to a web page. You can have a separate test that checks for ways to get to a web page. What do you think ?