The current implementation for dragging and dropping words or phrases in Scrivener is less than user friendly.
When you double-click on a word, thus selecting it, only the word is selected–none of the surrounding whitespace is included in the selection. If you then drag that word somewhere and drop it, you must then do two additional steps–you must insert a space to separate it from one of the two surrounding words where you dropped it, and you must go back to where it was dragged from and remove the now-extraneous space that was left behind.
The same is true if you double-click to select a word, and then shift-click to extend the selection to include several words, then drag the entire phrase to another location.
It would greatly improve the user experience if Scrivener was made smart enough that, when doing a select-entire-word(s) operation followed by a drag-and-drop, it would do the insert-proper-whitespace-at-target/delete-extraneous-whitespace-at-source for us. Also, when a drag-and-drop operation leaves behind extraneous whitespace followed by punctuation, all of the extraneous whitespace should be remove.