BS.
The App switcher (I think) should be cleared of all apps every once in a while to make it useful again. If you never clear it, eventually every app you own will be a "card" in the switcher, making it pretty much useless to use.
If you get one of those RAM usage utilities that show how much free and used ram is available, you can clearly see that having a bunch of apps suspended in the App Switcher DOES use up free memory. If you clear out the App switcher, all the free memory returns.
The only reason not to clear the app switcher is when you're trying to eek as much battery life as possible. But if that doesn't matter - I say, kill the apps you're not going to be using again any time soon.
Here's an example:
Here's how much free RAM is available on my iPhone with 21 apps "suspended" in the background in the App Switcher (41.8MB)
View attachment 1820852
And here's how much RAM is available after I clear them all out (352.8 MB)
View attachment 1820854