Can you improvise in one mood, one mode, one tempo, one texture, one rhythmical idea, one type of harmony for an extended amount of time?
Sure, you can.
But would your listeners stay engaged?
It's possible to fix your listener's attention using minimal technique without any contrast for a long time but it's obviously more difficult. You need to stay laser focused.
It's for people who have advanced mental skills.
In majority of cases, though, your listeners will become bored after about 1 or 2 minutes.
In order to keep people fixed to your playing, you need some contrast.
Change while you have the height of interest.
Then people will not see it coming. Then it will be surprising.
Then it will be a page-turner and a cliff-hanger.
You want them to forget to blink.
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