Hi and a couple of questions

[handrawn]

as I recall, using that tweak will usually alter the shape of your shape [] as nodes are removed, a reason I never really used it, but it depends what you are doing....

[handrawn]

again from memory - you can smooth a line using the tweak, but you only get one go immediately after you draw it whilst still selected; after that you would need to convert to shape first, as stated..
not always what you want to do

[Jonopen]

You're right, although I think by selecting nodes you can still go back and change the smoothing. Things can definitely go out of shape quite quickly, and you do have to use the slider rather judiciously. Not that easy since there's no numerical input option and whilst they've provided a 0-100% scale, it's only about 30px long on the screen. Like you said, it all depends on what you're doing.

[handrawn]

You're right, although I think by selecting nodes you can still go back and change the smoothing.

I checked - yes you are right - I think what I was thinking of is that you cannot compound this operation, you can only do it once for a given selection of nodes - but you can carry on with a different selection...