When writing an ad or a brochure (or even a blog post), repetition generally isn’t very helpful. You have a limited amount of time with your reader, and you need to make every word count. Besides, if you mention something once, you usually don’t need to do it again.
I’ve seen people try to apply that same logic to copy for websites. They’ll ask me delete an item or section on one page, noting that another page carries the same information.