It is my understanding that stims have two effects:
They work a bit like a recreational stim in that they make you alert, awake (or calm, with some types of ADHD) and euphoric. This effect can very much help with symptoms, e. g. in a euphoric state, it's easy to get on a task. This effect fades over time, very much like caffeine or a recreational stimulant drug.
But they also regulate noradrenaline and dopamine in the prefrontal cortex in other ways which may not directly lead to a heightened state nor effect the vegetative system, but help with many ADHD symptoms. This effect does not fade, possibly not even a little bit!
For the patient, it's hard to distinguish, and a patient may even "mistake" the "recreational high" for all it does, but it's actually kind of a side effect. I believe that this is where the notion of "needing a break" comes from.
The docs & society kind of wants us only to have the 2nd therapeutic effect anyway, and they only grudgingly tolerate that we might also get the high for a while, because we are not supposed to have good things.