Spacing with final option
Using the final option, I would expect the render to be the same as if the changes code was replaced by its arguments (or nothing in the case of deleted). Unfortunately, changes appears to interfere with TeX's space merging, causing
Minimal working example:
\documentclass{article}
\usepackage[final]{changes}
\begin{document}
This is a \deleted{short} sentence with \replaced{undesirable }{redundant} spaces
\end{document}
There is a double space between 'a' and 'sentence' and between 'undesirable' and 'spaces'.
This is easily avoided by being careful with where you put spaces, but mistakes that are not so easy to spot can creep up quickly.