(This post has not been written completely yet)
When the improvised melody is also a singing melody, one of the effects is that the improvised melody is not very fast any more.But what is more important is that the triad thinking-feeling-playing is better balanced during the improvisation. Fast improvised solos are not really followed by the emotions, that they follow its harmony (underlying chord progression) rather than the solo itself.
Therefore it is highly recommended to sing your improvised solos!
Actually one may say that he knows how to improvise when he knows how to whistle over a background with a chord progression and even an already existing different melody (something abundant to find in youtube).
Here is a relevant video.
https://www.youtube.com/watch?v=nxy9G-cs1aw&fbclid=IwAR3AunrtYys9ochaESosanXyt7YDM4sfJW7XqgY9J-a4ehhVCTL5ZsqE3aQ
