Well, I usually de-tension mine but occasionally forget. I figure its no big deal. But guess what? After three years I wore out the threads in the damn tensioner even though I lube them. Screw that, not gonna do that no more.
Chris, I have some education in metallurgy. Castings do not warp all by themselves, if one ever should then it is defective and I've never heard of such a thing. Iron castings should not even warp under heat and stress or they wouldn't make car engines from iron. The modulus of elasticity of both iron and cast or extruded aluminum is sufficiently great to withstand the rather low loads of a tensioned blade.THE AMOUNT OF STRESS IS INSIGNIFICANT. Cast iron has nearly zero elasticity and breaks before it bends. That is why engine blocks crack with even minute heat distortion. As for the tires, just depends on the quality of the material. As for the springs, any long time saw owner knows the answer to that one, but they weaken whether you relieve them or not due to changing load. They solved that problem with car springs long ago so poor quality springs is the problem with saw springs.