When shooting with film cameras with manual film advancement/shutter cocking, is it better to store it for a longer period of time with the shutter cocked or not cocked. Does it not matter? I'm seeking to prolong the life of my cameras
It is probably only advisable to enter tension in the system if your camera is being transported (e.g. travelling on a bumpy road), as some force may keep moving things in place.
Prolonged tension of springs may result in them "aging" (dislocations (errors) in the metal accumulate and eventually crack), see fracture. Tension can also result in creep. And if there are some bearings or other moving parts, they may not be designed for continuous force, too.
I would store it not cocked if held in a storage place. Note also, if you do not use it for a longer period, you may need to make some preparations (oiling/greasing), etc. to avoid eventual rusting.
It depends on the camera, but it probably doesn't matter all that much, especially for newer models.
Some medium format folks are religious about always keeping the works in tension. Some models only engage and link with the lens when cocked, and this linkage is key to whole works -- you can't even remove a lens without cocking the shutter release in some cases.
An SLR model doesn't have the same design, of course, but I was told to store my K1000 cocked, always. (I actually don't have a good reason other than habit, so I am interested in other answers.)
And Canon F models had a problem with squealing if stored cocked, so those guys had a ritual of always firing the shutter before bed. Again, this ritual may not be based on fact.
About the only thing folks agree on is that you shouldn't let the camera sit for too long between firing the shutter. For cars and mechanical cameras both, letting them sit for months without rolling takes a toll.
I suspect none of this matters much for modern SLRs. Most of the mechanics have been replaced with electronics, and the mechanics that are present are under the slightest tension, or are actuated using something other than stored kinetic energy, generally.