a bit extreme extreme, but useful to think what can happen.
In Africa on the very bumpy and rough roads, I always store the lens and camera separate when traveling. The vibration has been know to work the lens mount loose from the body. Doesn't happen quickly or often but still, why add stress to the system. So when I travel or store equipment for a long time, I do not attach camera to the lens.
I do this with an abdunance of caution.
I'm with RGF on this, a lot depends on the lens, but I have some definite rules for myself based on advise from others & my own experience.
Never transport Body & Lens (Any Lens) attached.
Never store Body & Lens (Any Lens) attached.
Always use a Blower on the Transition Face prior to Changing Lens (Reduces Dust incursion)
Some riders on the above.
When I'm shooting, I carry my Bodies/Lenses with Black Rapid Straps, all Bodies have 'L' plates, anything that has a Lens up to the 135f/2 attached, the Strap is attached via a RRS Clamp to the 'L' Plate on the Body.
Anything with a lens that is from say the 70-300, 70-200 or the Big Whites (200/300/400/600) I carry them with the Strap attached via the RRS Clamp direct to the RRS Replacement Foot (except the 70-300/70-200 which have Wimberley Plates attached).
All of the above is designed to keep as much stress as possible of off the Body/Lens transition, I have seen a number of situations where people have dropped their Bags, Lens/Body attached, and the Body has peeled away or fractured at the transition face, same when someone attaches a Large Lens then carries or fixes it By the Body, rather than the Lens, can result in the transition face deforming under pressure, once that happens you may as well spray paint the Body & hang it up as a lesson learned.