Obviously you know horizontal lines are not trend lines, right? Even when price is range bound. Horizontal TLs are considered trend lines per published books going back to the 20's written by the founder & masters of classic TA. Price can be congested/sideways, that is a trend. In fact a great deal of classic T.A. is built upon horizontal TLs that border various geometric price patterns. I never comment about option trading since I have no experience at it. I always comment on classic TA when someone's opinion is far from hard facts since I have been practicing the academic model of it for many years. And I agree with Xela about horizontal TLs being far more reliable.
Why don't you look it up yourself or buy a book on it? Here is a post from Peter Brandt - he is one of the market wizards 5 decades of strict adherence to classic T.A. as defined by Richard Schabacker (1930's). Look at Twitter yourself - this is not altered. This pattern, as many do, depended on price closing above the horizontal TL.
We recognize trend lines to identify areas of support and resistance. The angle is not the issue, support and resistance are the issues. Zela and comagnum are pointing out that horizontal lines can represent strong areas of S&R.
I wonder if Renaissance Technologies uses trend lines and if they'd raise their eye-brows if you mentioned them in an interview.
A cup and handle pattern with a horizontal line. Not a trendline. Where do you see the word trendline or TL? Where? And I don't need to look it up. You do. You made the claim.