I exported a part to print that was slightly tilted. I used the “Lay on face” command in Bambu slicer. When I printed 3 of the same parts the 2 circles at the bottom of each part lost adhesion to the bed on the same edge. It wasn’t sitting flat for some reason. I exported it again after I aligned it and then they printed fine. In the past I have exported parts, rotated them arbitrarily and used the same command and they sat flat. A good reason to stick around for the first few layers at least.
The “lay on face” thing isn’t always 100% reliable. It can get it wrong, though that’s pretty rare.
What I do when I use it is just quickly check the first layer right in the slicer to see if the full object footprint is represented.
My mistake for not checking the first layer… derp.
As someone pointed out to me once: PICNIC (Problem in chair not in computer). 
My misguided ass-umption was it would set the part to the bed flat. Of course that’s not it’s function DERP. It simply makes sure the part is touching the bed.
Well, it is meant to lay your object on one of its main “sides”. However, since it’s not taking the input from a CAD file with clearly defined faces but from a polygon object with many tris, it has to make assumptions and “guess” what the objects flat sides are. Easy with a cube, not so easy with more complicated shapes. Sometimes it just guesses wrong. Though most of the time it gets its right.
I printed a 90 AC duct and turned it on edge for less support waste. As I stopped rotating I noticed it automatically drops it to the bed.
Yes the slicer will always default to putting the lowest point of the object at bed level, which makes sense. You can override it by simply moving the object.
The lay on face tool helps rotating it to it’s most printable orientations.
I realized this morning first layer detection should have kicked in. It always does on my X1C. I just found out the X2D does not have lidar so no first layer detection. Not a deal breaker but it would have been nice to have.
I don’t think that would have helped. With the lay on face tool slightly getting the angle wrong, there was still something being printed as the first layer, just not the whole footprint. The lidar doesn’t judge your slicing, it just checks if what the printer has been given to print went down right. I assume it did.