Where documentary photography is concerned, selective manipulation by hand is typically frowned upon, unless the practice of it is clearly stated when the final result is presented.
However, in cases where a mask is algorithmically derived, purely from the dataset itself, without adding any outside extra information, masking is common practice even in the realm of documentary photography. Examples of such use cases are range masks (for example, selecting highlights only based on brightness), star mask (selecting stars only based on stellar profile), colour masks (selecting features based on colour), etc.
In some modules in StarTools specifically, masks are used for the purpose of selective sampling to create internal parameters for an operation that is applied globally to all pixels. This too is common practice in the realm of documentary photography. Examples of such use cases are gradient modelling (selecting samples to model a global gradient on) and color balancing (selecting samples to base an global white balance on).
Finally, it is also generally permitted to mask out singularities (pixels with a value that is unknown) by hand, in order to exclude this from some operations that may otherwise generate artefacts in response to encountering these. Examples may be over-exposing star cores, dead or hot pixels, stacking artefacts, or other data defects.
As a courtesy, when in doubt, it is always good to let you viewers know how you processed an image, in order to avoid confusion.
The Filter module's 'Fringe Killer' mode is an easy and very effective way to remove unsightly blue and purple halos caused by chromatic aberration.
A video is also available that shows a simple, short processing workflow of a real-world, imperfect dataset.
To only brighten the image (for example if you wish to bring out faint H-alpha, but nothing else), set this parameter to 0%/ 100%.
Whatever detail lies outside the RoI, is simply forced to conform to the stretch that was designed for the RoI.
Open an image stack ("dataset"), fresh from a stacker.
You can convert everything you see to a format you find convenient. Give it a try!