My humble opinion (on pipe lift off)

Aside from the technical issues,
The issue of pipe supports lifting off in the field is mostly a visual issue and usually results in some very important but technically incompetant client ranting and raving in your bosses office obout pipes left dangling off supports.
I find that in the majority of cases, the success or failure of the stress analysis input on the piping design is measured on a non technical and visual basis by 'tea break'engineers.
So, i generally try to make sure that the pipe sits on all supports, all the time.
Personally, i agree with the old engineering maxim of not letting support lift off. it just look bad.

Regards.