I was adding an "L" shaped wall cabinet Casework family to my model yesterday, and was surprised to find that I did not get a stretch grip at the end of one of the legs. I was also unable to use the Align tool to adjust the extend the length of that leg to the face of a perpendicular Wall. The family is set up such that the height and depth of the wall cabinet mass is set in the Type, but the length of each leg is an Instance Parameter.
I had successfully done this operation previously, but apparently with a different family. I was confused as to why it was not working, when it was clear from the object's properties that an Instance Parameter had been used for both leg's length. I edited this particular family (which I did not create) and found that somehow the Reference Plane at the end that was not responding had its Is Reference parameter set to "Not a Reference". After changing this to one of the other choices, the stretch grip was activated and the Align Tool was able to be used to align the end of the leg with other geometry.
After discovering the reason why, it all made sense. I have used "Not a Reference" on occasions where I have a Reference Plane in a family that controls the position of some minor geometry (such as the "swing direction" arrow of a horizontal slider in a plan view) that I do not want to use as an alignment plane in the placed family, but had never previously seen that value assigned to a Reference Plane that defines an important part of the geometry of the family.