Hearing aids have to be switched on whilst they're being programmed, and they go into feedback - very irritating after a minute or two, the high powered aids especially. Stick the end of the tube into a lump of blue tac and it stops the feedback.
Attaching the tip of an in-the-ear hearing aid to the 2cc cavity for testing, again to prevent feedback
And another vote for holding speakers to stands
Holding PCBs when I'm soldering