I run into this issue a lot. Often my analysis take some time to run. When I've finished the analysis and made the plots, the knitting part often take a lot of unnecessary time, because it needs to re-run everything. What makes it worse is that after 30 min of knitting, some error comes up. Although there are cache options, it's just not convenient to go through chunk by chunk to decide what to cache.
What I would like to have is to create html from notebook without re-running anything. The .nb.html files sometimes does that, but there are cases when it stops updating due to some knitr errors.
This is why I like Jupyter better since the .ipynb file can just be converted to html without re-running stuff.