I have personally never used spinners for speedrunning demos. I've used turn180 in Zdaemon though (Doom multiplayer port), where I do find quite a bit of use out of it. There are many situations where simply having a perfect turn180 helps you a lot. One obvious case is in deathmatch, where turning super fast to gain a tiny bit of time to mess up opponent's timing. In original Doom, one obvious case is actually Doom 1 E2M1 nomonsters/UV-speed/pacifist, where one can simply hit the turn180 key after picking the first key, blue key card, and get an easy perfect turn180. This turn is actually really difficult to optimize if you do the turn manually. It is so easy to lose surprising amount of time there. Like 0.14 seconds out of almost thin air. Also, the turn180 provides a lot of consistency which makes the turn trivial, instead of really difficult. Ridiculous.
I know there are other maps (pretty much all the maps to be honest), where I could use the turn180 key to make turns a lot more consistent and _precise_. The interesting thing about the turn180 bind is that you can use it for turns that are not 180 degrees. For example, you can use it for turns around 180°+-45° and be faster, as you can combine your manual turn with the turn180. It makes some turns a lot more consistent with some gained time. I have not used the turn180 in the past because I've always thought it is only for the keyboarders AND for the 'meme maps', where people just seem to be fine to use it. So a case by case ruling. Because the game is supposed to be fun, and spamming turn180 in a meme map can be quite hilarious.
Now, if the turn180 is allowed everywhere, we WILL be seeing it a lot in the coming speedruns of all categories. Now do we want such a viewing experience, where the runner may unexpectedly make a turn180? The turn180 is really tough to follow from others' perspective, for the runner it isn't that bad to follow, but unexpecting viewer will be like "what happened, I blinked and where did the guy warp to?". I've seen this happen many times online. If the turn180 is disallowed, almost nothing actually changes, because the turn180 is still rarely used to gain any significant advantage, except maybe in some meme maps where you gotta spin 180 every frame, but those maps (or complevels?) can be ruled differently.
I am sorry but who are you exactly? I don't think I've seen you ever engage with speedrunning or send any demos. This sentence alone is one of the biggest bullshit statements I've seen in many years. I don't mean to be rude, but the sentence just blew my mind how uneducated it is. I read your other comments and it seems like you do not have any clue about speedrunning. It is just that you are super clueless, and doing harm to the thread by derailing it a shitton. I will read your reply, if you have one, but I won't reply to you anymore to avoid further derailing. And please understand, I don't try to be mean.