A link to the quote would have been nice: Noise Reduction - RawPedia. The language could probably be improved for clarity…
If you read carefully, it doesn’t discourage you from using both sharpening and noise reduction in the same workflow. Observe the intention of the section:
This section details the order of operations for removing noise.
In context, the quote in question is the last step:
9. While it is generally not recommended to combine sharpening with noise reduction, RawTherapee-5.5 has a “contrast threshold” adjuster in the Sharpening tool, thanks to which you can sharpen details while preserving the smoothness of uniform, flat areas.
The while clause
– isn’t saying that you shouldn’t sharpen and denoise in the same workflow.
– it is saying that it isn’t recommended that you sharpen after you denoise.
– but you could sharpen smartly to recover from smoothing (and prepare for resizing).