Hi Joe,
Short answer: No, it doesn't really help, but that is probably my limited experience / understanding.
I do fully understand the issue of tolerances! What I don't understand or have any experience with is how other programs might build the tolerances into the
modelling process. I have seen only bits and pieces of how other programs work (e.g., in the course of YouTube videos where someone demonstrates how Fusion 360 was used to draw up a part or a whole project), but never in any of those bits and pieces have I seen anyone ever enter a tolerance into the modelling. (In the drawing that is made from the model, yes, but not in the modelling itself.)
FWIW, in my use of FreeCAD to date, I model things to "exact" dimensions, and then put in the tolerances when I produce the drawings. I would have thought this would be similar to the "old fashioned" approach using paper and ink - surely one of the master draftsmen of the past did not try to draw in the different possible locations of the edge of the part to allow for a +/- tolerance? Again, please forgive my ignorance - maybe this is exactly what they did, and I just haven't ever seen an example of it. And again I stress, I'm talking about the modeling (or in this case, the actual drawing) of the part. Of course, the designer must to take into account the potential effect of stacking of tolerances, and design and determine tolerances accordingly. But when this goes down on paper, the part is drawn just to one size, and the tolerances are added as text to that drawing - at least, as far as I have ever seen.
Actually, it would be possible in FreeCAD to build the model up using parameters (which I routinely do), including a tolerance parameter (which I have never done, but certainly possible to do). Let's say the tolerance for the parts is +/-.01mm. Put .01mm into the tolerance parameter, regenerate the model, and voila - now you see what the whole thing will look like if every single part is at the maximum possible tolerance. Put -.01mm into the tolerance parameter, regenerate the model again, and now you will see what it will look like if every single part is at the minimum possible tolerance. This would be possible ... but I can't think of a situation in which that would be worthwhile for my needs ... which of course may just reflect the limitation of my needs!
To go a step further, I would assume that the chances that EVERY part comes out at the same end of the tolerance are surely pretty low, assuming there is not some sort of system-wide error at work. One could create
multiple tolerance parameters to use in the FreeCAD model, even down to the level of a separate tolerance parameter for each and every dimension. One could then go through all possible combinations of tolerances to see what happens to the model. But now the issue would be the amount of time it would take to do anything useful with all of the various results. Let's say the project includes only 10 key dimensions across all the various parts, and each of those will be modeled at -.01mm, 0, and -.01mm. That will give 3^10 = 59049 combinations. I definitely don't want to take the time to look at every one of these ...
I know I keep saying it, but I'll say it again: all of the above may simply demonstrate my ignorance or lack of experience. I hope any respondents will receive this as my best effort to understand what it would mean to include the tolerances in the building of a 3d model (the building of the model, not the designing of the model), and have pity on my limited success!