Technically you can achieve the same thing with both options, but you could also show only highlighted lines, and then also use the filter box to narrow it even further
Typically, the way I use the "Show Only Highlighted Lines" option is when I already have some highlights turned on for highlighting lines with failures. That way, rather than having to type in "FAIL" in the filter to see only fails, and then clear the filter again, I can just hit the "Show Only Highlighted Lines" button, have a look, and then hit it again.
Hope that makes sense. Please let me know if you have any other questions at all.
