I don’t tailgate often, but when I do I can tell you exactly why.
There are certain people who will invariably try to insert themselves in that free space ahead of me then go 5-10 MPH slower than I was traveling. I can feel it in my bones when it is about to happen! So your theory that it doesn’t save me any time doesn’t hold water…those slow-driving morons do indeed cost me time if I let them in.
An example from yesterday: I maintained my distance and, after driving about 5 miles, at least FIFTEEN CARS had inserted themselves. the car that was once in front of me could be seen roughly 1 mile up the road!
I’ve said it on here before, but the large majority of oblivious morons drive white cars – don’t know why. And it is especially pronounced in white Camrys, with white Corollas running a close second. White Priuses I don’t seem to have a problem with, don’t ask me why. Shrug.