Thanks for all your comments, they help a lot.
First, as expected, I can see some problems with my workflow. I was taking a floor plan into SU, then an elevation, and coordinating them. There were minor discrepanciesā for instance, a wall 1/64" out of line. The snaps & inferences happened with different lines.
Second, while I'm currently working on a building, but I can see places in the furniture where small triangles did not close.
Third, the scale thing. I wasn't getting it before, but the bit about only closing in so far has been keeping me from getting close enough to see the problems.
On to the next: What's going on when Push/Pull will select a face, but will not move it? Or will only move it a certain amount, then refuse to budge? Or not move it until the mouse moves in just the right direction, after scribbling around trying to find any way that works?
Best,
JIm
PS: I'm in the States. What are millimeters?