>>6253076As far as physical feedback goes, the feeling of it spinning against your skin, the balancing you have to do to get it to stay spinning on a single finger, and the sensation of the centrifugal force working against you if you tip it a bit, are all amusing.
Not entirely related to sensations, but still very important - possibly the most important - is the fact that the act of spinning takes up small amounts of time, energy, and awareness. Translation: They stop you from being bored.
They also stop you from doing your usual boredom response that you might want to be training yourself to stop doing.
For example, you might start spinning your spinner in your pocket because you're spacing out, and normally in this situation you'd pull out your phone and aimlessly flick through social media... but you've noticed that doing that offers no satisfaction and makes you look like a bad friend/irresponsible employee who's "always checking facebook". Spinning offers something else to do that does not actually provide ordered input, but does keep you occupied enough to be more focused on other things.
Another good example is mouth chewing/nail biting/hair pulling/whatever gross shit you do. You can spin whenever your restless body wants to be fucking eating itself instead.
There's also the showboating aspect - they don't require any effort to use, but since they spin for like five minutes at a time balanced precariously on a fingertip, people assume you practiced this mad skill and are a master of prestidigitation. It's like how people learn to pen flip, except it looks crazier and requires far less effort.
And, still on the showboating topic, there's the "shiny new car" aspect among friends who spin - you can show off your model and make them jealous. Which is pointless, but people do it with even more stupid topics, it's human nature.
