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Saving selections in a channel
When i type text, then go to 'Text to path', make a selection from that path and save it in a channel, that selection is superior (more precise) to using 'Alpha to selection' and saving that in a channel, right ?
Warning, long answer...

The gut answer is no, it shouldn't matter... you should get identical selections. How to test:
  • create a text layer
  • Text to path, path to selection, save selection, rename channel to "From path"
  • Alpha to selection, save selection, rename channel to "From alpha"
  • Create white layer, get a selection from the "From path", bucket-fill
  • Create white layer, get a selection from the "From alpha" channel, bucket-fill
  • Create while layer, move under the text layer, merge down
You now have three seemingly identical layers. To compare them, make them visible by paris, put the top one in "difference" mode, which should give you a black image, then Layer>New from visible, look at the Histogram dialog. If you see just a thin vertical bar on value 0, then the "visible" contains ony pure black and both layer are identical. Otherwise there are differences (use "Curves" to make them more visible)

On my Linux, there are absolutely no differences between Alpha and Text, but there are noticeable (using the histogram) differences between the Path one and the other two. So, the alpha and the rendering of the text agree (which is expected since they are really the same thing). So for you the alpha could be what you call "more precise". However, on some platforms, if you have sub-pixel rendering enabled (almost always in current systems, in Windows it is called ClearType IIRC), the Cairo library used by Gimp will render the image using it, sometimes creating weird colors in the outline (this is very visible when you create white text over a black background). In which case, even if text and alpha agree, the real shape is the one from the path... But in that case, I create the text layer, get the path, delete the text layer, create a selection from the path, and bucket-fill it. This circumvents the outline colors, and then Text, Path, and Alpha all agree...
For some reason, alpha to selection, turned into a path, always has some inaccuracies (which does not happen when i use text to path):

Ah, but you aren't comparing selections but paths... of course a path from a selection will be less accurate that the path that created the same selection. There is a second path-from-selection with a big set of options (shift-click the "path from selection" icon at the bottom of the path dialog) but it is vastly undocumented.
I know about the advanced path options, but as you say, its undocumented, so i have no idea what to do with it (and there are a lot of options...!).
So for now it seems, turning the text into a path and from there into a selection is more accurate.

But its also always an extra step, which is a bit tedious.

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